Momentum is when you go really really fast, and then turn off your engines, but you still slide forward from the previous speed. Basicaly, you still hae momentum, but you will start to go slower and slower because there is no constant forward thrust.
Regarding the pilot tool, it... seems way to good.
Im good for 25% less damage. Would be a good tanking tool... but i feel it would be too strong on some ships. It just seems like something super strong on junkers and galleons. While all the other ships better off with other tools.
And it does make impact bumpers kinda useless. Combine impact bumpers with this, and you pretty much got a squid ramming rampage.
Impact bumpers today does have its uses sort of like this allready, defencively, Offencively. And in combination with Drogue chute to negate as much impact damage hitting the ground.