You should be afraid, very afraid. It would be quite easy for a high lift/jackall to **** you if you don't know what you're doing. A fellow rover owner got smacked by one a few years ago. Had to be airlifted out of the boonies, ended up loosing an eye.
Find someone who know's what they are doing (I can't tell you how to know they know). Use it some under lighter loads, pay attention to where the forces are, raising and lowering. Lowering a load is one place the handle can fly up and do a number on you. ALWAYS keep your hands on the handle, your head out of the way, when the handle is anywhere other than the fully up position. Be ready to jump.