Made by Ruger for the semiauto pistols. I have the Mark II 22/45 so I did not have factory holes. Took it to a gunsmith, 3 holes and $45 later had it mounted. I was able to keep the factory sights on and the profile is low enough to use them if something happens to the optics mounted on the base. Because I left the sights on I also had the gunsmith trim about 1" off the base to make it flush with the start of the barrel. Very happy and I knew I would need the gunsmith work to use.
Pros: low profile, Ruger made
Cons: long if sights kept on
This review was written in the old system and had content requirements that are different than reviews written today.