I personally wear a clip carry only around my property and immediate area. I have had the clip ride up and almost out of my pants at the store. I'm sure there are technques to make it more secure, but I prefer my 640 "slick" in a good holster when out in public. The clip is indispensible though when just hanging around close to home. I just clip it on my pants or into my back pocket and it is easy to take the gun off and put back on when changing modes of activity. The only gun I have the ClipCarry on is my S&W 60 and it is my dedicated "knock about" gun at home and never sees a holster.
I don't think it is the complete answer to replacing a holster but it does have its place when putting on a holster just isn't appealing or sometimes even possible (Sweat gear, beltless slacks, etc.)