I was considering holding out for a Thunder Ranch 940 because it's brown lol, but biggest pro is the direct mount optic, like your new 590 Thunder Ranch version. Just got an A300 Ultima Patrol and wanted an optic. So I removed the rear sight, installed a Skalarworks Sync2 mount and chose a Holoson Paralow 503 which mimics an Aimpoint mini (got ACSS reticle).
I'm mentioning my experience because there are many other gun enthusiasts buying shotgun optic mounts that sit low as possible, are strong and have a good rep. Waye better than a rail mount. IMHO Mossberg nailed it with a direct mount optic for a shotgun. Excellent choice.