I've been mucking around with MSh builds and it is actually quite a nice build. Not even so much for shotguns though. It's an every-weapon build, more-or-less, with shotguns being a major component of it. It also has excellent "extra-building" potential, where you can dump HR->DM in for some active defense, Fin->WK for some modding abilities, grab Int(2) for some perfect knowledge or just dump any traits you need/want as the situation and finds warrant. It just makes you more versatile whilst bringing your shotguns back up to mid/late game speed without becoming an unbalanced/singular weapon type build.
Fair enough, MAD is still my favourite shotty build. But Shottyhead gives you an every weapon platform. You never know what the game will throw at you, so the instant weapon switch, quick shotties and faster run/reload speed just lets you take the game as it comes. Get good mods? Go down the WK path and mod up a nice selection of weapons and armour. Good unique? Build towards its use. It doesn't really excell at anything, it just does a bit of everything, where it might just come together as more than the sum of it's parts.
It looks like a shotty build. It even has the word "Shotty" in the name. But really it's more of a generalist build with good options after the build is complete, but it makes it so that your shotguns don't begin to suck too badly in mid-game. Actually, the tactical shotgun does some pretty good damage at 1/3 fire time, probably out-DPSing most other build's shotguns except in high armour situations. Plus you can mod stuff up nicely at the end, which is something that you can't do with MAD.
I like the whole Fin->Jug->HR->Rel->Rel->SM->MSh way of doing things. Early weapon speed/swapping to get through the Arena/Court, faster big-booms with a slight auto-dodge for mid-game/wall/special levels and then back to fun with shotguns. Plus it's a real bonus to fire off 2-3 blasts of your tac shotty, knock them the hell out of blast-radius range and then whip out your RL/ML and start exploderising what's left. You've got a weapon for every situation as long as you've got the ammo and mods to make them shine.
You've got pretty much any play-style you want, all wrapped up in one nice little loose master trait. Even pistol builds work, as long as you recongnise the fact that a Shottyhead's pistol is actually called an Assault Rifle.