Its crazy for a carry gun, but for HD I could see the sense for the very same reason. If you practice using the blade in that form I suppose it might be useful. I'd prefer to just carry a knife seperately, but some might like it for a nightstand gun. In reality its probably just for guys to show there friends.They have been doing it for centuries with good reason. In close quarter combat when you run out of bullets you already have the knife in your hand.
It was initially made to be something funny and to catch people's attention at shot show.