I heard good things about them. They recieved top marks after "cast lead". Quite the reliable optic, just about undestructable. The problem with the M21 is the reticle and the washing out. Both of these problems are non-existant with the Mars.
I've heard some bad reports but everyone has their opinion and mine should be taken as such. Ultimately I don't see the Mars as being worth what they want to sell it for. Not a slight against CANAM, the manufacturer wants too much.