I love my mustang 2, use it all the time.
As far as the USB goes, it's an audio device on your computer and you can record direct with it. I've done several recordings late at night direct to the computer while listening through headphones, it works great. I use reaper, btw - the recording software that comes w/the mustang is not that useful.
Also, make sure you download the latest fuse and mustang firmware from fender:
https://fuse.fender.com/
As far as tones go, I find the tweeds sound great, the blackface great and the others are OK. Not crazy about the pedal effects but they are functional.
Here is a side by side comparison I did w/a drri and a mustang 2 DR model.
FWIW, I've since since traded off the DRRI.
Here's some random tracks down w/the mustang. No, they're nothing great, but for a something done in my basement just goofing around, more than adequate.
http://wagner-usa.net/tunez/mrmustang_mixdown02.mp3 - two lead guitars, one with some over the top chorus
http://wagner-usa.net/tunez/funkewag.mp3 - super-sonic model