I'm with @simon1, I'd prefer the extended tube magazine. That's what I'm familiar with and trained with. Rather have the higher capacity over the quick reload. Load as you shoot, stay topped off.
I can't remember when I've shot empty the tube magazine of a shotgun, even with a 3-round limiter. Topping off the magazine isn't difficult. The 870 DM doesn't gain much capacity and still needs a tube for the slide, so ... why?
Another pass here. My 12 ga. holds five rounds and I rarely bother putting more than round in the tube. I figure. One possible follow up shot at most when hunting.
It would have to be a 10 round mag to even consider it. Would still have to work out the manual of arms in order to single load a different type shell, such as changing from buckshot to slug rapidly. If it required removing and/or switching the box magazine, that would be a tactical no-go for me.