I have a B&N Nook Tablet running CM10 Jelly Bean.
iRb works fine.
When the tablet is in horizontal, I prefer the layout on my ICS generic Chinese tablet better.
I'm not sure why there is a difference in layout but assume it is the operating system.

imho, using any low power tablet to read chords is not going to be a problem. iRb runs smooth and fast. Maybe if you use the tablet for band-in-a-box accompaniment, you might find some dissatisfaction, but I wouldn't anticipate problems.