The Umi is very, very, very comfortable. They really don't feel like they weigh anything on your head.
That being said, they do that swivel thing for sure but I believe Jeffrey had said he's developed a better headband and I think he'd be willing to ship out the better headband to reduce the swiveling. Or, if you're buying it new (sounds like you may be?), I'd ask him about the headband before picking it up. He's super responsive.
The sound is very pleasing. Honestly, if I was to put it in words, it's neutral and analytical but with a subtle mid bass boost. It's clean from top to bottom and it takes EQ very well (I added a small bump to bass on my amp's tone control and the bass can be as satisfying as the JM). I think the difference in the rosewood version is subtle vs the silver one I have. It may be worth asking him about it if that's the look/set you were thinking about.