I've had my Colorfly C4 for 10 days now and I am impressed. I do not own (but have used) an HM801 so I can not give an in depth comparison of the two. I will say that the Colorfly C4 is all that I hoped it would be. I've had to recode some of my highest quality 24/96 Flac to 24/192 .wav, which was no big deal. I purchased the C4 mainly to listen to Flac at 16/44 anyway. I can say that the upsampling of 16/44 Flac to 24bit/192kHz on-the-fly works flawlessly and sounds beautiful. I almost did not buy the Colorfly C4 because some of the post in this thread, especially ones that said the metal/brass face was really plastic, this is absolutely NOT true, the face is metal with a brass effect finish, and at least on my C4 is flawless. The Black Walnut backing never fails to get a "wow thats beautiful" response from those that I've let hold it. The interface does not take long to get used to, and is intuitive after a few hours. There is something about the esthetics of the Colorfly C4 that appeals to me, a warmth that the plastic looking HM801 lacks. The quality of playback was essentially indistinguishable from the HM801, at least to my humble ears. In the end, the Colorfly C4 sounds astonishing (and is a benchmark in mobile HiFi) and appealed to me (like a classic Leica camera would) in appearance and internal components. I am a very happy C4 owner.