my son is into airsoft scrimmages. i sometimes try out his accessories on my sig 522 and also on my FNH PS90. he recently has an eotech clone that i just tested on my ps90 at the range a few days ago. it held it's zero just fine. i'm going to purchase an eotech XPS clone for my my sig 522 with a 5x magnifier. the problem with the green lasers are their adjustment screws cannot handle the repeated recoil on the 522. i fixed this with pouring melted candle wax into the screw adjustments.
the slings/grips/grippods work fine but not all clones are built the same. i've seen cheaper grippod clones fall apart during scrimmages. i have an authentic grippod and my son's grippod clone holds out just fine. normal airsoft velocity is around 300 to 400 fps. scrimmages restrict it below 400 fps and close quarters battle is limited to 300 fps. bb weights also differ. airsoft guns get more expensive because they are being made from metal instead of plastic (internals and externals).

my son is 13 at the center of pix. those magazines hold 300 bb's but empties out real quick on select fire.
http://www.youtube.com/watch?v=NWGrDxqL70cvideo of his new M4 shooting in the backyard
-a|ex