I had the M6 for quite some time, I've upgraded since to the Schiit Jotunheim which is truely amazing.
The M6 was definitely one of the best buys I made, it's a really good value for money, in my opinion it takes both the Fulla 2 and the Audioengine D1 which I also own by having more clarity.
The only thing that annoyed me a little is that it doesn't play nice with my tube amplifier I tried connecting it to a Little Dot MK IV SE but there was a lot of static noise to a level of being unusable I figured it must be because tube amplifiers are much more sensitive and prone to having static, but it seems to have something to do with grounding (this uses standard 2 prongs 100V-240V AC to 12V DC without any third grounding prong) with other amplifiers which are not tube amplifiers it worked just fine.
I would definitely recommend this to anyone wanting a nice entry amplifier to the world of headphones amplifiers, it can drive almost any headphone even the more demanding HD6XX which has 300 ohms of impedance.
Note that out of the box on windows it only support up to 32 bit with up to 192Khz and in order to get 384Khz you have to use DSD (not that much of headache).
Also I had the older model of the M6 with the only difference that the newer model (this model) has a remote which is a really nice touch instead of pushing the tiny joystick to use it.