I have a very old one, one of the first when H&K still imported them. It was very stiff at first and needed a lot of shooting dry firing to smooth it out some. They have pretty bad triggers but dry firing can help a lot. You need to keep forward pressure on the forend or it will start back (great for upland or waterfowl but not necessarily for turkey hunting) and you can lose your target.
The chrome-lined barrel and plastic exterior, for the most part, make them good all weather guns. The bore is pretty tight compared to many other guns and anything from .640 to .655 seems to work well, all other things being equal. It's really all about the internal geometry of the choke of course.
I shoot a good bit of Hevi-13 through all my guns, including the Nova. I like #6 or #7 shot. I'm not a real fan of the Magnum Blend shells but lots of other people are.
I'm getting ready to start the evaluation of Winchester Long Beard shells with about 30 different choke configurations and the Mobil system that the Nova uses will be included.
Thanks,
Clark