Have tried two, one was a two stage bright for daytime, but dim for night, open tube so could shoot with left eye closed, found it easy to accquire targets, other was OEG, made by Webley, needed both eyes open and enough light to illuminate dot, cleverly gave small dot when close to eye on rifle, but dot appeared to increase in size when further away on pistol. Found it difficult to judge range and holdover compared to scope, but if used in ambush from known range worked well. IMHO. David