I actually have two of them. The other is mounted on an AR-15. Both have worked out well, holding zero, with a 4 inch dot that does not "over power" the target. The auto brightness works well. The sight comes with a set of zero dials similar to what is on a scope, but I just mounted the sights, seen where they were hitting, the adjusted by trial and error. The adjustments have separate locks that keep the zero from changing. The only feature I don't like is having to take the sight off to change the battery, but battery life s excellent as long as you turn the sight off when done, and don't store it with the sight turned on, in sleep mode. The top of the line Aimpoints and EOTECH's are a little better made, but no where as small and lite as the Fastfire, and not designed for slide mounting. For me, speed and accuracy are improved over iron sights.
Larry