My grandson has one and it’s pretty cool. You soak tiny beads in water which then swell up. These are loaded into a clear plastic hand grenade sized bottle. The bottle is then screwed into the top of what resembles a machine pistol. The toy then fires the water pellets rapid fire till it jams or the pellets are gone, pretty cool. The teens probably put the swollen pellets into a freezer, makes the pellets hurt on impact .
Yes, if you get hit with one that’s “normal” it’s just annoying. I’m sure frozen ones are worse.