man, the invisibility is to overpowered in the single player.
you can pretty much go anywhere you want with invisibility, come across a safe spot where noone can see you every 30 metres, switch, regen to full energy in 2 seconds and switch back.
could be standing directly infront of a soldier with invisibility and be jumping around and they wont notice you. in MP invisibility really only works if in shadows and completely still, and the moment youre out of energy youre screwed if anyone is nearby and has armour mode on and full.