I got an iPad and onsong and am in the process of getting it set up.
It seems to work well but I haven't used it on a gig yet. I'm the bass player and only sing backup, I shouldn't need it but:
I'm old and can't remember shit. Esp with at best a once a week practice with 20-30 originals and more coming all the time, plus about the same number of covers. I need a memory jog from time to time and I'm not gonna keep a book and music stand on stage. The pad is much less obtrusive, and beats the heck out of scribbled notes taped to my upright.