I have a marine magnum and love it. I don't think I'd love the synthetic any less though. When I bought my magnum, I was actually looking for the synthetic, but all they had was the marine magnum, and I wanted something then and there.
I have noticed if you want accessories to match the nickel finish, it might be a tad difficult. I added one of those elastic shell carriers to the buttstock, and thats it.
I'd agree, unless you have a need for the protection of the finish, might be wise to go with the synthetic and save $$$. But then of course, I've bought many an item based on its cosmetic looks rather than raw need. So if you REALLY want it, and got the $$, do what makes you feel all warm and fuzzy on the inside!