Gen2 and Gen3 also have an improved (in this instance it is an improvement) bolt release. In case you aren't aware do NOT lube the piston or it will cause reliability issues. I have a Gen2 and oh my the thing just keeps on going. I tested mine with 1k rounds of LE Fed 00 Buck and LE Fed Slugs with no cleaning. Then pumped the cheapo Wallmart 100 round birdshot value packs and not a hickup. Great SD/HD shotgun.
I'm running mine with MagPul stock with Aridus adapter. Love that stock. Works great with 1301.