I've had these dummy grenades before. I actually practiced throwing one a few times, letting it get scratched up. Two things I noticed:
1.) When the pin is fully engaged and bent-over, locking it in place, it takes a LOT OF FORCE to pull the ring/ pin out and arm the grenade. The first few times I tried, I could not do it, and had to reposition my grip and arm movements for better leverage. Of course, I wasn't in combat and no adreneline was flowing...
2.) The goal is to throw these things 30 yards or about 100 feet. You HAVE to get them more than 50 feet away, since that is the effective killing radius. Throwing them 30 yards away is pretty easy out in the open, but in the woods, once in a while you'll hit a tree trunk or limb and the damn thing will hit the ground way short, about 20 feet in front of you.... (not good).