With a good holster [for you] IWB carry is quite comfortable with a size larger pants, or maybe with the button undone, and just the belt holding your pants on. With any significant pistol, a belt is pretty much necessary for comfort, and to keep both sides of your waistline at the same height. Without a belt, a pistol with any heft to it will sag the waistband.
Uncle Mike's Nylon Clip-On IWB
Little to no retention. I stopped carrying with it before any of my pistols hit the floor/ground, but I think it would have happened eventually. I also caught the clip bent out beyond where it would catch the belt. If the gun doesn't come out of the holster, the holster+pistol may squirt out of your pants. There are variations on these holsters, some from other companies.
I would steer clear of this type of holster. Some people carry with clip-on holsters all the time, but I'm using belt loops from now on.
Uncle Mike’s Kydex Paddle Holster
Click Here For Review
Fobus Roto-paddle (GL2 Model)
Click Here For Review
It held onto my Glock real tight, to the point that I could rip the holster out with the gun, despite a tight belt. I found the holster to be uncomfortable, and nearly impossible to conceal with because it sticks out quite far. I haven't used it in years. I can see how the rivets might fail to hold it together.
I think I'm going to cut it apart and use the Roto bit for a DIY competition holster.
I think mine is a Generation II. It's a very fast holster, but quite uncomfortable. It seems to pinch me if I don't have a shirt tucked in behind it. The shirt tucker adapter adds two thicknesses of 0.09" Kydex between the pistol and belt, which makes it hard to conceal. I tried sticking felt to the holster, but it's still uncomfortable. Some people love them. Someday I will get around to selling it.
Fist leather IWB #19A
More comfortable than the Sidearmor, but it's thicker, so it's still not very comfortable. Really holds onto the gun tight, but would likely loosen up if I really worked at it. It really rides too high to conceal even the small Kahr I bought it for. It wasn't cheap.
I’m going to fix this holster as soon as I get the Kydex and
UPDATE 8/1/2010: I did fix it, but haven't really used the holster. If I'm going to IWB carry, I carry the Glock 26.
Gould and Goodrich Leather Belt Holster
It looks very nice, resembling a duty holster, and doesn't conceal well. Like the Fobus, I'm constantly hitting it with my forearm, and smacking it into things. Might make a decent range/IPSC holster, but an open-front Kydex holster would be faster.
Glock "Sport/Combat" Holster
Basically it's like a pancake holster made of a plastic that feels a bit like vinyl. Conceals well, but the material is rubbery and holds onto the gun a bit too much to be fast. I like the holster, but have not used it since I bought the next one on the list. I still use the matching Glock-made mag pouches all the time.
Crossbreed Super-Tuck IWB
Man, I love this thing! Comfort is similar to the Glock-made "Sport/Combat" holster, and it's a bit faster. It will conceal my Glock 26 under a t-shirt, as long as the shirt is long and big enough. I've had one of the belt loops break, but didn't notice until I went to take it off. The holster is pretty ugly, expecially if you trim the leather away from the grip. I can reholster with one hand, which is pretty essential to me. If I had bought the regular Crossbreed IWB, I would probably have not broken the belt loop, and I've never tucked it in anyway.
Crossbreed Super-Tuck, Part 2
Crossbreed Super-Tuck, Part 3
Uncle Mike's Nylon Pocket Holster
I carry my Kahr PM9 in this most of the summer, and occasionally for family outings. It was pretty floppy, so I epoxied a plastic card to the bottom. Like the Crossbreed, it ain't pretty, but it works. It's the only thing I feel really comfortable carrying during the summer. . . all the time.
UPDATE 8/1/2010: The old Blue Cross card on the UM holster broke into several pieces eventually. I made my own custom Kydex pocket holster for the Kahr.
Galco Ultimate Second Amendment Holster
This is a tuckable IWB made of horsehide. I inherited this one. It rides low, which makes concealment easier, but trying to get the stubby G26 out of it is a bit difficult, requiring scooping it out of your waistband a bit before you can really get a grip on it. The belt hook would seem to be made for 1.25” belts, but works with 1.5” belts, and holds onto the 1.5” belt really well. This may be the trick to getting J-clips to work; order for a belt the next smallest size. There are a couple strips of leather sewn into the holster to serve as a sight track, but nothing to hold the holster open after the pistol is drawn. Reholstering requires two hands and some delicacy when the pistol is loaded. I use this holster sometimes when I want to slip on something more comforting than my PM9 at home.