Opinions vary to be honest; some people swear by crash bungs, others wouldn't touch them. I've read tales of bungs digging in when a sliding bike leaves the track and causing it to flip and sustain much more damage, but who's to say that a footrest digging in wouldn't have the same effect?
For stationary and low-speed drops they're excellent, though SDs don't have a lot of fairing plastic to damage compared with a race rep. I had them on my 2004 ZX-10R and the only off I had on that was coming out of a slow-ish bend in 2nd gear when I hit the coolant that a "mate's" Benelli had dumped when it spat out a core plug. It's the most graceful and painless crash I've ever had, a very un-dramatic lowside. The R&G bung didn't prevent the belly pan, ignition cover or right-hand rearset from being damaged, but it prevented damage to the handlebar, brake lever, middle and upper fairing panels and the mirror, so they paid for themselves. For the record, my "mate" was contrite and offered to pay for the damage, then changed his mind two weeks later and refused to pay for anything. Tosser.