Looks very cool. I helped my dad sight in his muzzleloader last weekend. It has a thumbhole stock like that, and I really liked it.
I've been thinking about looking at a different stock for my Mossberg. It's the 500 sluggster in 12 ga with a rifled barrel. I'm feeling really good with it now that I've had it a few years, but I think I'm going to put a pistol grip stock on it to help improve the accuracy.
"When a hunter is in a tree stand with high moral values and with the proper hunting ethics and richer for the experience, that hunter is 20 feet closer to God." ~Fred Bear