This is a Holosun Technologies Red Dot known as the 507K, model HS507K-X2.
From The Manufacturer:
The HS507K X2 is an open reflex optical sight designed for concealed carry pistol applications. The X2 Series pistol optics feature two improvements. First is the addition of Lock Mode from our 2018-2019 LE pistol optic models. Lock Mode, when activated, locks the buttons preventing inadvertent setting changes. Second, the buttons have been redesigned to compliment the Lock Mode by placing them lower and out of the way. Additional features include Holosun’s Super LED with up to 50k hours battery life, Multi-Reticle System, and Shake Awake.
