I've had the Tuck-N-Go from Galco for about a year now, and don't wear it often. The main reason behind this is the fact that a pocket holster just makes perfect sense, but also because of some other things. The Tuck-N-Go is an Inside the Waistband (IWB) holster that you can tuck your shirt over top of, making it extremely concealable. The J-hook is minimalist, making it even more likely that it will go unnoticed.
First off, this holster is high quality, very well built, which is what you would expect from Galco. It's also good looking. The rough surface of the leather it is made from faces outboard to give some purchase for when you draw.
It's a tight fit at first, so you want to keep your heater holstered in it for a few days to loosen things up a bit, maybe even put a sandwich baggie over the gun to help the leather stretch. One of the features is a steel insert at the mouth of the holster to facilitate reholstering, so that when you smoke the tangos from the door of the Blackhawk using your quick draw, you can reholster with one hand while you attach your tactical operator retention lanyard with the other.
For those of you looking for a cantable holster, this ain't it. Drop it into your waistband, hook the J-hook under your belt, tuck in the shirt, and you're good to go. It works very fast if you're taking it out of the glove box or such and want to carry into a store. There's just not a lot of fuss with putting it on, but do know that you will be loosening your belt a notch or two to make up for its width:
Keep in mind that the leather wraps up and over the steel insert in the mouth, so the width of what you see here is not what goes inside the waistband. One of the problems I have with this holster though is that even the little bit of width that this holster has with the pictured Kel-Tec P3AT, you can see the bulge of the piece on your side:
It's not a big deal once you tuck your shirt in, but it's there. I don't know how in the world people carry in their waistband over their appendix; that has to be the most uncomfortable way to carry ever devised even if you can get over having a loaded weapon pointed at your satchel all day. The rough checkering of a Kel-Tec will chafe the soft bits of your jelly roll too, so wear a wife beater or another T-shirt under the one you intend to tuck over the gun or you'll be sorry.
So overall, I would rate the Tuck-N-Go as extremely high for concealability, and low for comfort. Drawing from this holster is about as slow as it can get even if you don't tuck a shirt in over top of it, as it sits so low to your belt line that you can't get a firing grip on it. Trying to do this in a hurry can make you drop the gun. Once you tuck a shirt in on top of it, the draw time gets even worse, but remember that this is supposed to be a "deep concealment" holster to enable you to carry in places where you otherwise would not. Speed of the draw is not what was intended with this concept, for sure. I see this holster as being one of rare necessity, where you want to carry but can't, and need some sort of option.