The Hades Arrow is essentially a water rocket with a CO2 firing mechanism, so when you drop it down the "mortar" tube it activates and flies out like a real mortar shell. The projectile weighs a quarter of a kilo when it activates, and presumably greatly reduces in weight before it hits the ground (because it is a water rocket and uses water as a propellant, gradually expelling its fuel as it flies). With all players on a field wearing helmets I'm sure this would be perfectly safe, but I certainly wouldn't recommend getting whacked on the noggin' without something protecting it. Nor would it be fun to stand in front of the tube and get half a pound of water-filled plastic to the kisser. But if you see this and all that comes to mind are safety concerns... I think the fun centre of your brain is broken.
So who's going to buy me one?