Mossbergs do not work well with any sort of pistol grip. Hold one and try to move the safety to the
fire position while maintaining your grip.
If I were going to get an HD Mossberg and money were no object, I'd get this:
It's a 590A1 with GRS & speedfeed. I'd get the light barrel version because it's not going to be subjected to military abuse and the heavy barrel is
heavy.
In the real world, I bought one of these on sale at Big 5 and added GRS to it:
because even after adding the sights, it cost hundreds less than the 590A1.