FWIW, I just bought a Supernova and am very pleased so far. Many people on here claim the Supernova (and more the Nova) rattle real bad. I'm sure some do but the one I bought doesn't rattle a bit. I can't even make it rattle. I bought it used too so if it were going to rattle it should be doing it. It's actually feels really good and tight.
The one I bought has the Steadygrip too. I love it, it feels great! I can't compare it to the 870 stock but I did handle a 835 with the tactical stock on it and it didn't feel nearly as good.
Just my 2 cents...