My dad gave me an 3" SXP he won at a DU banquet, I grew up on 870's so I think I can help a little lol. When they say smooth they mean SMOOTH!!! I've shot Wingmasters and Expresses and they're no comparison to how smooth the SXP pumps. There's also no slide catch when you pull the trigger like on the 870, as soon as the hammer falls that slide is moving. I didn't even realize I had pumped it, I'm sitting there trying to pull the slide to the rear thinking it was jammed but it was already to the rear waiting for me to push it back forward. 870's if you have back pressure on the slide you have to let up a little to release the catch in order to pump, a long time user will do this automatically without thinking about it. I used the SXP most of the time I got to hunt last season, and I was still having some learning curve issues. The other problem I had was that I ended up short shucking a couple times too trying to get used to that slide. It's a great gun, I love it, but it's definitely a different beast than the 870. The parts fit is good, mine's camo'd and it looks good, but I haven't seen one naked. It shoulders well and is pretty ergonomic.
Tough call, the first season with an SXP he might have some issues, but any shooter can overcome them with a little practice. 870's are also very good shotguns, and you can't go wrong with a Wingmaster. If he's OCD about rust, I'd stay away from a Nova, my buddies extractor spring rusted and he could never keep it from being rusty ever again. That's the only thing I've seen bad about a Nova, but I haven't shot one.