The only thing I don't like about inside the pants holsters is that it makes my belt line uncomfortable. It may be a fat boy thing or just OCD thing but I don't like feeling tight.
Also, the one very important thing is the quickness of the actual draw. If it takes you 15 secs to bring the gun out because it got snagged under a shirt or with the belt, the gun does you no good really. I even have what's called a "belly band". It's designed to be worn like a girdle and it has a sewn "holster" and even has a mag holder. It goes under your clothes and you're supposed to draw by loosening up a button and sneaking the gun out or something. It's a great idea, but it too is uncomfortable and the gun is really not held tightly at all. It's like a super hide-out holster in theory. Uncomfortable as hell in reality.
Believe me, I've tried and have a ton of different holsters. The most comfortable overall to me by far have all been paddles. The Fobus one I use frequently is all plastic, which makes it really light weight. It stays tight, so there's not to big a bulk sticking out (unless you are carrying a big gun).
BTW, the Clip Draw pictured above I've seen first hand too. It's also great in theory, but the draw back IMO is that it's something permanently mounted to your gun. In other words, it won't work in your regular holsters after you install this piece because it screws into the slide and is gun specific if I remember correctly. I think it would have the same effect as an inside the pants holster.
I saw one that used a fake old school pager at the top as a "handle" and the gun/holster sits inside your pants hanging down towards your groin area. I see it at the gun shows all the time, but it seems to only work if you wear loose slacks...
