If you got it in the last 3 years it's a gen2 with the larger porting. The gen1s were much smaller holes and more of them. I can pull up pics later to show the differences. Officially there is no gen1/2. Just differences in the holes, but some guys are using gen1/2 to discriminate the two. If it's a new in box gen1 you will get more for it then your asking. Probably 350 or more new. Just because they aren't made any more. Not that they perform better. I have both and they are identical performance.
Here is a pic of gen 1.
And for anyone who hasen't used a MAMS it's by far the best all around AR muzzle device. Someone needs to buy this!!