I like my 930 JM Pro (don't love it). I bought it back in October for 3 gun and it has been pretty good. As far as slugs go? It shoots them into about 3" groups about 2" high-left of the target at 50 yards (which is where most smoothbore shotguns shoot slugs).
Now, for the bad:
1. When I purchased the gun I discovered that the magazine tube where the extension connected was dented. Not just a little dented, but to the point that the follower could not make it past. The gun was essentially a 4+1 gun instead of 9+1.
2. After ironing out that problem, I discovered that the stock follower was a piece of junk.... I scrapped it for a GG&G follower which has worked well since.
3. There is a piece in the bolt carrier that you really should stake. Before I did it would get loose and rattle, and really made reassembly a pain in the butt.
All in all, it took me about 2-2.5 months to get the gun to run reliably, but since then I haven't had a problem.
A little good news to finish it off:
Even though the gun is now "used", I can still make a decent profit if I wanted to sell it
*I have about 85 slugs, 30 buckshot, and 1200 birdshot rounds through my gun as of now.