I have one, it works great with the lighter Semi's. Mine fits my M&P. The straps and supports are wider than the cheaper shoulder holsters, so it distributes weight better. That said an M&P and 2 mags all day is heavy on the neck muscles by the end of the day. I wear it when I am going to doing something that routinely exposes the midriff and I'm not looking for someone to see a gun. It works with jackets, loose fitting sweat shirts etc, but is obvious with tighter fitting stuff.

As you know from looking it's not a cheap set-up. I would be a little concerned the weight would be an issue after say 4-5 hours with a 40 0z or so gun, unless you have a specific need for it, OWB's are better carry IMO.

As for the moon clips, I'm no help.