I have the Holosun 403B, has the auto on off, 50k hours of operation, shuts down if sitting still for at least an hour which is adjustable to stay on 8 hours. Small, compact, clear, brightness adjustable, easy to adjust. I have one on an AR as well. Last one was $139. If you are concerned about a unit being fragile or lacking in longevity, buy from Brownell's, no hassle returns on virtually anything except ammo.