I hear that... Kinda what i was thinking.
Hmm... 14 shots, 15 if you have an HK missile (probably not), coming out of an exterminator sound dead tasty... and they all are strong too (and ap 4) except maybe the stubber. Have to pick one up for apocalypse now, the vanquisher can wait. Or maybe not, the vanq looks so much cooler.
Also what about accuracy? a battle cannon misses half the time, but half of the 9 HB shots are going to hit. So maybe the HB's are more accurate, but less dangerous? I'd rather be hitting with a Str 8 Ap 3 marineswatter than 9 HB's in a lot of circumstances.
Another point is the Turret mounting, the HB can technically see behind because of the 180 degree ruling on sponsons, but only one will be able to see it half the time. That means you have to be dead on to see with all the shots. It also makes the stubber better because its in the turret. I guess you get a free swivel-on-the-spot when you shoot... thats what makes a basilisk work.