Depends on how it’s structured and used I guess … IMO I don’t know that IO is any better or worse than an equivalent fully-amortized ARM.
Assuming even the pathetic 3% annual raises that seem to be standard these days, you’re looking at about a 27% increase in income at the end of an 8-year IO period. I doubt the increase to a fully amortized payment is as large as 27%.
(Rate shock is another matter entirely, of course.)