I have to admit they don't work all that well outdoors.
If they land in deep grass, my grenades are unable to blast pellets through heavy grass. Try laying your AEG on it side in the turf and see how far you can shoot.
It's just hard to blast through vegitation with 6mm plastic pellets. I could have cranked up the juice, but the grenade would become dangerous in open area as there'd be no grass attenuation.
There aren't many issues with crap invasion. The monobody design of my grenade resists fouling. The few places where dirt can get in are ports where a lot of gas and bbs are blasted out of so in a sense it's self cleaning.
My design is also corrosion resistant. The only rustable part is the pin. It might even be dishwasher safe, but I wouldn't but a propane filled grenade in a hot dishwasher.
Want nearly free GBB gas?