I have a few of their books and I've found them to be really great. I haven't tried their app, but for as much as they want for it (even with the discount) I find it irritating that they still expect you to buy the books:
"Trails are fully documented in FunTreks, Inc. printed guidebooks (previewed but not sold in this app). "
It also sucks that for those of us who own both an iPad and an Android phone, they want us to buy the app twice.
With that said, I can definitely recommend their books.