I've been using my HG310 cabs for over a year. Tweeter is the best I've ever heard in a bass cab. I love that they are sealed -- it's the main reason why I like them much more than the CN210 and CN112 cabs I'd used previously. More comments below.
I'm spoiled by the NV610 also! As I've said dozens of times, it's the best cab I've ever owned or heard. I use it every chance I get, however it's too big for half of my gigs, and I also leave it at home when there's a tricky load-in. The reason I chose HG310s as my secondary rig is that they are light, modular.... and sealed. They have the sealed punch, but then they also have that neo vibe. They are DEFINITELY NOT an NV cab. I can get the HGs to sound very good, but my ears will never like them as much as the NV610.
Not in my experience. I've used the HG310 in many dodgy situations (I'm a jack of many bar bands), and they actually sound better than the ported cabs I previously used in those same situations. My first thought is it's because they are sealed, but it's probably more complicated than that.
I'm no audio engineer, but the only negatives to the rear placement that I can imagine are as follows: you might lose the benefit of the rear speaker when playing outdoors where there's no reflective surface behind you, or when the rear of the cab is placed against something like a heavy curtain.
I try to keep the cab at least 10" from the wall. The speaker cable pretty much guarantees 4", but I don't know the minimum recommended distance. @bebass , do you know?