Historically, the hedgehog was a very effective Anti-submarine weapon. It could be fired forward, so SONAR could maintain contact. A hit almost always meant a kill.
Regarding the model weapon, I'll quote a Queens Own member from another forum:
Umi RyuzukiThe "hedge hogs" were typically launch tubes set at a 45 degree angle just in front of the Destroyer's bridge. The could lob a set of bearings about 20 yards down the pond, and then drop them into a hulahoop. The loading mechanism was kind of an upsidown "y" shape. the straight side acting as the chamber and barrel, and the short angle in, the magazine. The magazine was arched down and then up behind the chamber. The Chamber held about 8-12 rounds. each time the "Hedge Hog" was fired, the rounds would exit the barrel in front of the bridge, and the blow back air would force the magazine rounds back. When the rounds in the magazine rolled back down, about 8-12 rounds would drop back down into the chamber, and be set for the next volly. There was not really any penetration force to the rounds other the gravity. Sinks on submarines were all about proximity, and referee decisions.
As I understand it, the idea was to fire a small burst of bbs upwards at a very low velocity and a high arc like a mortar. If the shots landed close enough, the combat director would call the submarine sunk.