The ISTD technique books are really intended more as references for teachers in training, and in the workplace, so they can make sure they are serving up kosher technique.
That said, once you learn their language, you can as a student read them, refer to them, and get quite a bit of benefit this way.
There are other books which say more, including one by Arthur Moore who wrote the original version of what became the ISTD book. The thing is that the more a book says, the more controversy it generates and the more misunderstanding it gets blamed for.
Basically, you can't learn dancing from a book. With good in person trianing, you can reinforce, extend, and maintain you knowledge in part through the aid of the books - but they are not a solution by themselves.