Most of the ones I have are Bianchi for my 9's and 40 and are leather with the snap tops.
The open top single stack I have for the Sig Pro is by Tripple K.
I do have one uncle mikes older nylon double stack that too works well.
Not sure what you want a mag carrier for. "Before you say to hold and carry a mag, were you not paying attention."
I mean do you want it for targets like a steel shoot where time is a paramont and opening tops slow you down.
Do you want it for an IDPA shoot or CCW where you are not going to carry many rounds but just have a back up to meet the shoot rules or for CCW. But do not want to print that you have not only a gun but spare mags.
Three gun where making sure the mag is going to bee there after you run, jump, flop, and get back up and move on with the rifle or shotgun and where you are going to carry many mags as well as other gear.
As you can see each application has it's own set of challanges to make the carring of spare mags easy and fast to get out but keeping them there till you are ready.
I have found that the double snap tops work for me in IDPA, three gun, and steel shoots. When I carried Most of the time I had a P230 and simply stuck a spare mag into a Nylon flap that looked like a Leatherman or folding knife sheath. I guess a Super Leather man case something that size would hold a compact double stack for CCW and not holler GUN.
