The Firearm Blog guys shoot an MK760, which is a low-budget copy of the S&W 76, which is a copy of the Swedish-K.
I don't really know why the old-school tubular submachine guns required such a long receiver length, given the short length of the pistol rounds they fired (this includes the STEN, Sterling, MP40, Grease Gun, etc. Basically everything until the Uzi came along with its telescoping bolt).
In any case, this thing looks like a heck of a lot of fun to shoot, and seems pretty controllable. Given that it's likely a seven-pound 9mm, that's not hard to believe.