erennert i dont know if you were looking for styrak to awanser this, but form first hand experecne owning 2 jg m4s's one pre 08 and one 08, ill tell you everything the diffrence i found form the 08 and the befour was the gear boxes had the diffrent bushing. Outher than that they both have barrel wobbel even if you get it and it does not it will devlope it quickly also the sock will wobble over time easyer fix though just have to tighten the screw in the stcok, also they are know to have way to much gresse i opened my 08 to put in after market parts it needed to be cleaned out. Also thei si a diffrnce in clour form the body to the parts its allmost if the body looks a shade of grey. as for the good side great to upgrade but imo the d boys is much better as it dosnt have any of theys problems and they also dont suffer what their drop in metal bodys have with their mag problems their pre bulits are great but its up to you jg is solid i belive they surpass tm any day IM.
EDIT and the diffrence form the m773 i know this is carrying hadel isnt detachable!