Oem magazines tend to be the most reliable since manufacturers spend lots of time and money doing their r&d in order to put out a reliable product. Factory magazines can be spendy especially from companies such as Sig Sauer, HK, FN and the list goes on. The Factory P320 magazines generally run around $49.99. I found some aftermarket magazines made by ACT for $29.99 each so I thought I would give them a try. I have heard others talk about this brand in the past and they swore by the ACT magazines working great in their Smith and Wesson M&P's. Not all aftermarket magazines tend to be reliable, so I recommend if you are thinking about trying some aftermarket magazines in your carry gun, definitely test them with your practice ammo and carry ammo to make sure they are working as they should before carrying them. ACT only make one size so far which is unfortunate. So far they are just making the 17 round magazine. I have been using them in the Compact 320 which has a shorter grip frame which causes them to stick out. For this reason I haven't used them as the primary magazine in the gun when I am carrying it. I have been carrying them for my reloads though, the added length makes them easier to snatch out of the mag carrier. I have been using them in my training with quite the variety of different ammunition from Wolf, S&B, Magtech, Blazer Brass and Speer Gold Dots and all ammunition has worked well in them. I took them to a class last year and also did not encounter any malfunctions. So far I am pretty pleased with their reliability. It would be nice to see ACT release some 15 round flush fit mags for the compact P320 in the future. From my good experience with the 17 round mags, I would definitely give them a try. Have a safe and great weekend!