Manufacturers come out with new refrigerators every year and the most reliable company 5 years ago might be just average today. Also, every company will have good models and bad models so instead of focusing on which manufacturer to buy from, it's better to look at specific refrigerator models instead. Of course, best selling doesn't always mean best quality or most reliable.
Double stacked magazines give you about double the magazine capacity of single stacks, but they are slightly less reliable for two reasons. They are more prone to drop jumbles and the ammunition loses alignment and won't feed without fixing the problem.
Additional mounting holes allow the user to configure the carrier with a belt clip, tuckable strut, or carriage via a device like the Pocket Shield (not included). Designed around the full-size Glock 9mm/.40 magazines, the carrier will also fit most popular double-stack pistol magazines, like M&P, P320, XDM, and HK.