Aimpoint's ACRO was the first fully enclosed pistol red dot sight. As such it meant no debris or snow could occlude the reticle dot display light as with traditional red dot pistol sights. Then a year later came the similar HOLOSUN 509T ("T" for the titanium body) and is creating a loyal following, including this shooter. AIMPOINT ACRO-> FULLY enclosed red dot sight, MSRP $600.+ or - HOLOSUN 509T-> FULLY enclosed red dot sight, MSRP $499. + or - *solar screen as alternate power source *circle/dot with options for either or both *titanium body *side pull-out battery tray *"Shake Awake" turn on feature and auto off after 10 min. of no movement *50,000 hours of battery life on setting 6 with CR 1632 battery So with all these features and its proven reliability and strength I prefer this sight to all other red dot sights. (See YouTube's "Sage Dynamics" drop test for proof.) I predict other major red dot sight manufacturers, like Vortex and Leupold, will soon have their own fully enclosed red dot sights. Eric B.