Thank you! And yes I think you can use the jetpack when charging, but without any movement penalty. This is because there is a sacrifice in the power of the weapon due to your jetpack using some of the energy as well, and you also won't be able to jetpack very far, so it will be fair to use this as a quick retreat when your plan fails, or are taken by surprise. However, I didn't think about losing a leg, so maybe the movement penalty won't apply in that situation or just significantly reduced, but that may make the upgrade to reduce the penalty obsolete until you die and respawn, but those are just my thoughts.
But yeah, this weapon is not meant be used to pick off a single enemy one at a time, no, its recommended that you charge the weapon to it's full potential and eliminate a massive group of enemies with one blow, which is why timing and position is important, so you land the attack at the perfect moment before the enemy gets close enough to kill you. A great risk, but with great reward! This is why I think this weapon will be very fun to use and very devastating in the right hands.