This is a Sticky Holsters Magazine Pouch known as the Mini Mag Sleeve, model MMS.
The Mini Mag Sleeve is a IWB or Pocket magazine or accessory holder. This is designed for small single stack magazines. Fits magazines similar in size or small than a Glock 43.
Features:
Ambidextrous
American Made
Latex and allergen free
Multi-Use and Multi-Fit
Part of a modular system
Fits magazines similar in size or smaller than a Glock 43