I use Pierce +0 extensions once-in-a-while, but most of the time, I use the flush mag. When my GAP floorplates arrive, I have a feeling I'll be using them all of the time.
For me, the +0 extensions are concealable, but I prefer to carry at 3:00, and they poke out just a hair. They don't offer very much in the way of retention during the draw, so I generally don't bother using them. I just carry my 19 if I want a bigger grip.