chess ebook apps

I really like the idea of having different books on my phone or ipad along with board on the screen playing through the moves.  I saw some apps were coming out before I took a break from chess and I was hoping just about all books would be available in this format now.  But it seems that's not the case.   

If anyone uses or has used some of these chess book ebook viewers please let me know what you think?

I am sort of afraid to buy any books this way because it seems e+ chess books may have been a scam.  Can people who bought books through this app still access them? 

Anyone like using any of the other apps or are there different/better formats for learning chess that have supplanted this?