I received a Fulla for Christmas to use with my M50x's. I absolutely love it. Immediately, I heard a soundstage and detail difference on my cans compared to my iPhone 5S and 2009 MacBook Pro. This is my first DAC, so I can't compare it to anything else, but I really like the added detail, presence and warmth it brings to my headphones. My girlfriend has a new retina display MBP that has a decent DAC, but the Fulla bested that as well. I did need to buy a Belkin powered hub for it to be recognized, but the hub itself doesn't need to be plugged in. Have also successfully used it with my iPhone.
One thing people aren't talking much about is the fact that the DAC chip in the Fulla is the exact same as the Schiit Modi. Just something to consider if you're a fan of that DAC.