If it can teach you JSP in 24 hours, it must be pretty good .
I have had a few 24 hours books in past, and I found they were pretty good for quickly coming up to speed with a new technology, if you know another similar technology. And most of the code examples are really simple and easy to follow. But I wouldnt use those books for studying a technology that I am going to work on with every day.
For example, If I am experienced in JSPs, and I want to get a quick idea of ASP, perhaps to do a small 2 page website, one of these books would be helpful.