Wow, controlled hover with a rocket. (Score 1)

Very tricky, indeed. This is harder than it appears at first glance. Anyone can set off a time release bomb that blows it's wad, propelling a ballistic projectile into the air, but it is a bit harder to either: [ (1) stage a series of rockets to create equilibrium with gravity or (2) use a single rocket with a controllable thrust. ] But then you have the problem of attitude adjustment (keeping the rocket's business end pointed at the ground without wind resistance/fins keeping the mechanism pointing straight) and horizontal movement, also while keeping attitude adjustment in check. On top of that, add 25Kg of mass. Not an easy trick at all.