I have them on all my handguns carried for defense, and am happy to endorse them. They are not precision aiming equipment, especially on guns like 640s with no actual rear sight, but, provide a big, bold, bright reference for aiming at ranges at which civilians have any business firing at bad guys, or at ranges where dangerous wild animals are too close for long guns. I recommend combining their shallow vee rear "express sight" with the front Big Dot on any platform that will accommodate it. And, take a look at other products, such as the tritium illuminated front post for ARs/etc., and social shotgun sights.