I have used a Fobus paddle for IDPA. No problems whatsoever. I also use Fobus paddles for CCW. How good they are for you will depend on your build. If you're skinny and bony, there may be a chance it can slide out. If you're big and fat, then it's doubtful it will move at all. I had mine move some when I tried wearing it with a skinny cress belt. Dumb idea, but I wanted to see if it would work. Go with a wider belt, and it will hold it holster quite well. The type of cloths you're wearing may have some affect on them as well. The best thing to do is simply go try one out.
As for mag pouches, I think the Uncle Mike's is a better unit. It has a tension control screw that really works well. It stays put, but you can still adjust it for whatever tension you want. I think a belt type mag pouch is better than paddle. There's alot less surface area to resist pulling out.
To be honest, I haven't checked out the Uncle Mike's holsters yet. I probably will try one out for my CZ-75 I just bought, because the Fobus unit is really for the Beretta 92. It fits securely, but just seems kinda wierd.
Ross