BudsGunShop.com - 590 compatible?

Rob, no Sir. The DM's have a proprietary design currently. mossberg.com/category/series/590m-mag-fed/

No, they're both different, proprietary systems and the mag by itself is not a direct fit for the 590DM.
I can say however that I recent;y spoke to the folks at Adaptive Tactical and learned that they have a venom kit in development for the .... drum roll please ...... 590 Shockwave ! Which based entirely on the fun-scale will be a must have for me.
(If you're reading this folks at Adaptive Tactical....please also make one for the Remington Tac-13, and I'll buy that one too)