I don't use a Sneaky Pete for my P3AT, but I do use them for a Sig P290 and a Colt Combat Officer (3" 1911). I would think the SP for the P3AT would be very nice. I carry my P3AT in the original rug with a spare mag under the grip. When carried in the back pocket, this prints wallet. With a SP, I expect people would think you have a large format cellphone, like the Samsung Galaxy Note II.
The SneakyPetes for these other pistols are huge. But no one seems to notice them. And the few that do, they do not know it is a holster. Usually people think I'm a geek and it is for holding a small iPad. If you can deal with the geeky look, they are great.
The SP has an insert in the case. I remove the insert and put a spare mag under the grip, like my P3AT. In the case of the CCO, two of the 6 round mags fit side by side in the space.
The quality of the holsters is very good. I do not know why they have a low rating on Amazon. I guess I need to go put a review up.