i personally love the nerf football design. light weight projectile and has the longest range from what i have seen so far.
the football them selfs are soft and durable, so they can be recovered and reused multiple times.
not a fan of the bottle rocket design. using it during the winter would suck, not only can the water freeze, but the spray it shoots out the back will soak the operator.
im not too sure about the use of a tornado grenade. yea people can use helmets, but what about other areas where it can do damage? getting hit on the shoulder/back/chest, would definitely hurt someone. but that is only really a concern if the chute fails.
the way i see it, there are three main factors to judge which design would be most practical.
cost of projectiles and the life span of their use.
weight/material used to make the projectile, needs to be durable, light and soft enough to prevent blunt force trauma.
and of course, performance. how high, far and accurate can the shots go. can the range be duplicated consistently enough that a range table can be worked out and used to direct shots.
seems that the nerf football design fulfills all three, and since there are two different sizes of balls, the smaller one can be used as an infield mortar, whereas the larger football would be used as a howitzer, providing indirect fire from base camp.
also i freaking love the whistling, it just adds to much to it, and would add another layer of safety, as you can hear the round on it's way in and do what you need to take cover.
Weapons Technician / Gunsmith
Don't look at me, I don't know, lol ¯\(°_o)/¯.