Are you asking about the red dot or the Holster?
The Red dot is a Trjicon RMR on a Glock 17 9mm.
The holster is a Milt Sparks Optics Ready holster. Super comfortable, straight drop. Conceals nice. I use the holster both for guns that have an optic on the slide and ones that don't. I just really like how comfortable the holster is.