I have one and use it when I can't carry IWB. Like Skiprr said, it's great for crowded 'huggie' activities where the wrong person putting a hand on your gun could cause some problems. Mine is comfortable enough to wear all day with a compact gun and spare magazine. Drawing is slower and I would recommend using a 'stall' EVERY time you use a public restroom (you should do that anyway). BUT, having a gun that is a little harder to get to is much better than not having a gun at all.
FWIW: I went to a concert one time wearing a SmartCarry. I was stopped at the entrance and asked to lift my untucked shirt and empty my pockets for security. I had a tiny 1-1/4" folding knife on my keychain. I had to give it up to get in. Nobody detected the SmartCarry. So, I went in with a 9mm and 26 rounds of ammo but no knife.
Everyone needs a SmartCarry, OE..........,
