It all depends on builds. Anything with Juggler lets you shotgun swap till your heart's content. MSh especially. Anything else, then the Tac Shotty is a godsend, even compared to a T-combat shotty. Just tactically speaking. Sometimes you really can't afford that 0.2 secs, especially in a group of mixed enemies.
I like it anyway. If I was going to carry any off-build assembled weapon and a stack of ammo to go with it, it'd be a tac shotty. Then again, P+T are really handy mods, so I'd carry a combat shotty if I didn't have it tac'd yet regardless. It's a good upgrade for any build. It's like the missile launcher of shotguns, anyone can use it well. Everyone can use rocket launchers and combats shotties as well, but the ML and Tac Shotty are definitely upgrades that are build independent, and can be pretty reliably gotten or made every run. Although, I've had plenty of runs where I finally got my mods for it 1 level before the mortuary, so yeah, sometimes that upgrade comes pretty late.............