This is the third "On demand" book I have brought and I will have to say I'm beginning to get quite impressed. I teach software products for a living and these books are now ones that I recommend to students. They have, in my opinion, three main strengths:
1. They are well-written introductions to the package and they have good illustrations that show off the feature or process being described in a way that makes it easy.
2. The technical explanations are sufficient to explain what's going on with overloading the reader with tons of information.
3. They can be used as a reference book after you have done the lessons. This is very useful because many teaching books are not particularly good as reference books once you've finished them. I keep these to hand for reminding myself on bits I have forgotten.
They are also inexpensive compared to other similar books. They are fairly thin, but contain all the info the learner wants; and they are in colour throughout which makes learning easier.