I've had these headphones for several months now, using them via BT on my phone and via the wire on my laptop, and I'm extremely happy with them.
Pros: excellent sound, noise cancelling works well, being able to plug them in via wire, comfortable on my ears.
Cons: not as much volume or bass as my PortaPros, BT delay not great for watching videos, sometimes there is an odd pressure when using noise cancellation.
Niggles: No play/pause/forward/back functionality when wired, buttons don't always respond on the first press, shipped with a battery cover that wasn't properly attached.
These points in more detail:
Sound - As I said the sound coming out of these is excellent. I hear sounds in songs I've never heard before, and the overall tonal balance is very good. As I also mentioned, though, they are not bass heavy and I do miss that from the PortaPros, but tbh the tones from the 310s are more balanced and allows me to hear more. I think I actually prefer hearing more of the music over hearing heavy bass.
Sound Volume - They could be louder, but again like with the bass, I don't actually mind and now that I've gotten used to it I think I prefer not blowing out my ears. No need for me to bring on premature hearing loss. :)
Noise Cancellation - This works quite decently, I've used it to muffle out street noise or in the office when I wanted some quiet time. It doesn't cancel out noise 100%, of course, but it certainly makes a difference. They do, however, sometimes have strange artifacting that feels like extra pressure on the eardrum, it usually doesn't bother me but in a few rare environments it's been amplified enough for me to turn off the noise cancellation.
Fit - My ears are usually pretty sensitive to headphones, both in-ear and over-ear, and I've always had troubles finding headphones that fit comfortably. I loved my PortaPros but they would usually start to hurt after an hour. Although the 310s initially caused a little discomfort when I first got them, this went away after a few days and I can now wear them for hours without a problem. Whatever foam they use in there works great.
BT Reception - Bluetooth isn't perfect and I have on occasion experienced cut-outs when I've stuck my hand into my pocket covering up my phone. But this isn't entirely unexpected and the cut-outs have been so few that it hasn't bothered me. There is also a slight delay in the BT reception but again, it's not an issue if you're listening to music or playing most games. Watching video, I would imagine, could be annoying.
BT Functionality - All the buttons work with the most recent iPhone updates, forward, back, volume, play/pause, etc. Often I have to push the forward, back or the play/pause button twice to get it to register, I'm not sure if that's because of connectivity issue or some "feature" I don't understand to prevent these buttons from being hit by accident. Not a big deal, really.
Wired Functionality - I love being able to plug these in so as not to use the battery up, or to get rid of the BT delay. I do wish I could play/pause or switch songs while these are plugged into my iPhone, but that functionality is missing unfortunately.
Build Quality - I had a small problem with the USB cover not being attached properly and had to spend 15 minutes with a jeweler's screw-driver to sort it out. That aside I think the overall build quality is excellent.
All in all, I love these headphone and think they're worth the money. Sure, there are a negative points, but I can be pretty picky and they are outweighed by the positives imo. Highly recommended.