I like 'em, within their limitations. The new model's ability to shoot .45 LC out of the shotgun bbl is interesting.
There is (or, at least was) an accessory scope attachment plate that attached via two drilled and tapped holes in the receiver. Buy it and attach it. Leave it there on the off-chance you want to use a scope or NVD. This was a hard-to get accessory from Springfield. Once you attach it, you'll hardly notice it's there.
Remove the screw at the toe of the butt stock, and replace with a threaded sling stud, such as from Uncle Mike's. The underside of the front sight lug has a hole for the other sling swivel. This means you'll need 1 threaded stud, 2 QD sling swivels of your choice of width (1" or 1 1/4"), and a matching sling.
Numrich has a two compartment case (in fall camo, no less) that was originally made for a Savage combo rifle/slug gun. The two padded compartments close with snapped flaps, and the case has carry handles. Look in the web gear/bags/etc. section. It's cheap, and perfect for the M6.
Oh, yeah. I'd go stainless. If you need to, blast bead the thing, and paint with a suitable spray from Brownell's.
Hope this helps.