From what I understand of Rupert's Drops, it would probably depend on how they were attached to the shaft whether the exploded on firing. The weakest part of the drop is the long filament, as soon as that gets broken the entire thing goes. I think the bulb would be a little more sturdy.
That said, I'm sure there's actually as much of a shrapnel effect as you think there it. Unless they're specifically firing them directly into the enemies eyes or thereabouts, it wouldn't do that much damage. I mean considering these guys are holding them with thier bare hands and breaking them:
Which btw, awesome video /\ highly recommend watching it all the way through. Destin does a great job breaking it down.