I have only used kindle reader on the touchpad athough I installed a couple of others. The kindle app works pretty good and calibre was pretty easy to use (requires another app kindle import) It is a two step process but easy enough.
Other formats depend on the software apps your friend is using and his level of knowledge of how the software works.
Best go with the kindle app in my opinion as many other apps are not as nice and you could spend days figuring out which is best.
I had the kindle app up and working an hour after I onboxed and charged my touchpad
and I played with the web browser first.
Helen