They're loud, but you can see how quickly he get can his hands out and pull a pistol in the video. This wouldn't be used if there were a dozen guys with rifles actively defending, but it seems a great way to board a ship if the crew is incapacitated or just refusing to lower a ladder. One guy with a pistol would be enough to keep a lightly armed crew at bay for the few seconds it takes for the other marines to climb the ladder.