I debated for quite a while on running an open top mag carrier. I've always used Safariland leather closed top. I switched 8 months ago to Bianchi's Accumold Elite open top carrier and love it. I've had absolutely no retention issues, which was what I was worried about most. I've been in several foot pursuits in that time in where we ended up on the ground and at no time did a mag come lose or even my extra key I keep.

Side note, I rock the Vickers base plates on my mags and it is a perfect combo.