The hole looks like its an afterthought, it was added when they realized the fin was hitting the duct on the propeller. Its not going to hurt propulsion much.
Overall, the users look slow. But then they also don't dolphin kick that well.
It sounds like they have a sensor in there that turns on the motor when it detects you are kicking, so it's sort of a booster. There are bicycle boosters that work the same way, they run when you pedal.