I thought about this a little more, and it's interesting to consider which of the two moves are more "optimal".
My initial thoughts were based on points - namely, with the book answer, you can avoid seki without having to fill in your own points to capture, as described here:
Suppose we go with the suggested book alternative. White has the option of threatening seki, forcing black to capture. Black fills in two of his liberties in doing so.
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O 4 |
$$ . . . . O X X X 6 |
$$ . . . X O O X . X |
$$ . . . X X X O X 3 |
$$ . . . . X O O O X |
$$ . . . . 1 2 7 O 5 |
$$ ------------------+
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[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O 4 |
$$ . . . . O X X X 6 |
$$ . . . X O O X . X |
$$ . . . X X X O X 3 |
$$ . . . . X O O O X |
$$ . . . . 1 2 7 O 5 |
$$ ------------------+[/go]
6 captures + 1 point - 1 capture by white = 12 points
Alternatively, with the book solution, we don't have to fill in the marked intersections, and can avoid seki completely.
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O 2 |
$$ . . . . O X X X 3 |
$$ . . . X O O X . X |
$$ . . . X X X O X C |
$$ . . . . X O O O X |
$$ . . . . . 1 X O C |
$$ ------------------+
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[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O 2 |
$$ . . . . O X X X 3 |
$$ . . . X O O X . X |
$$ . . . X X X O X C |
$$ . . . . X O O O X |
$$ . . . . . 1 X O C |
$$ ------------------+[/go]
5 captures + 4 points = 14 points
Even if white captures the two stones and black throws in, it's still more than the 12 points achieved by the alternative move.
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O 2 |
$$ . . . . O X X X 3 |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . 4 5 . O . |
$$ ------------------+
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[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O 2 |
$$ . . . . O X X X 3 |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . 4 5 . O . |
$$ ------------------+[/go]
6 captures + 4 points - 2 captures by white = 14 points
Ko Threats
But then we can consider the idea of ko threats. Even if we can avoid seki with more points using the book's solution, do ko threats change between the variations?
With the book alternative move...
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O . |
$$ . . . . O X X X . |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . 1 . X O . |
$$ ------------------+
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[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O . |
$$ . . . . O X X X . |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . 1 . X O . |
$$ ------------------+[/go]
White can use the seki-threatening move as ko threat #1, inducing black to play at the marked spot:
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O . |
$$ . . . . O X X X . |
$$ . . . X O O X . X |
$$ . . . X X X O X C |
$$ . . . . X O O O X |
$$ . . . . X W . O . |
$$ ------------------+
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[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O . |
$$ . . . . O X X X . |
$$ . . . X O O X . X |
$$ . . . X X X O X C |
$$ . . . . X O O O X |
$$ . . . . X W . O . |
$$ ------------------+[/go]
White can play his sente here for ko threat #2...
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O W |
$$ . . . . O X X X . |
$$ . . . X O O X . X |
$$ . . . X X X O X X |
$$ . . . . X O O O X |
$$ . . . . X O . O C |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O W |
$$ . . . . O X X X . |
$$ . . . X O O X . X |
$$ . . . X X X O X X |
$$ . . . . X O O O X |
$$ . . . . X O . O C |
$$ ------------------+[/go]
And here for ko threat #3. If black responds to all, white is now captured without ko threats in the area.
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X W |
$$ . . . X O O X . X |
$$ . . . X X X O X X |
$$ . . . . X O O O X |
$$ . . . . X O C O X |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X W |
$$ . . . X O O X . X |
$$ . . . X X X O X X |
$$ . . . . X O O O X |
$$ . . . . X O C O X |
$$ ------------------+[/go]
So maybe 3 ko threats or so...
Now what about the book move?
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O . |
$$ . . . . O X X X . |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . . 1 X O . |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O . |
$$ . . . . O X X X . |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . . 1 X O . |
$$ ------------------+[/go]
Supposing white follows the order given above to illustrate point difference, white can make a ko threat similarly to the alternative book move threat:
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O W |
$$ . . . . O X X X C |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . . X X O . |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O W |
$$ . . . . O X X X C |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . . X X O . |
$$ ------------------+[/go]
Later, white can capture as another ko threat (#2). To avoid seki, black throws in:
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . W C . O . |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . . W C . O . |
$$ ------------------+[/go]
White can threaten to move out with ko threat #3, but does black even need to answer?
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . W O X . O . |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . . W O X . O . |
$$ ------------------+[/go]
It's hard to say. Maybe if there are white stones nearby to the left, white could play like this to link up to the left of the diagram:
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . W . O O X . O . |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . W . O O X . O . |
$$ ------------------+[/go]
So maybe to prevent this, black responds to the ko threat:
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . B O O X . O . |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . . . X O O O X |
$$ . . B O O X . O . |
$$ ------------------+[/go]
If there are nearby stones, then, maybe white has another ko threat here, for a 4th ko threat:
$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . W . X O O O X |
$$ . . B O O X . O . |
$$ ------------------+
- Click Here To Show Diagram Code
[go]$$Bc
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . . . . . . |
$$ . . . . O O O O O |
$$ . . . . O X X X X |
$$ . . . X O O X . X |
$$ . . . X X X O X . |
$$ . . W . X O O O X |
$$ . . B O O X . O . |
$$ ------------------+[/go]
I can't see the "3rd ko threat" in this situation as being a threat unless we know that white can get enough liberties by escaping to the left. So perhaps depending on this, white might possibly have an extra ko threat using the alternative to the book move.
In that sense, perhaps playing solidly eliminates this possible ko threat (if it exists), at the expense of the two points required to fill in order to capture and avoid seki.
In general, I like being able to keep the two points by using the book solution. However, it's true that this leaves aji and an extra possible ko threat if there are nearby friendly white stones...
Interesting problem!