I have the Violectric Chronos. I struggled to find reviews of it too. I've actually never heard the DFR so can't make any comparisons on that front. But the Chronos is an interesting beast. Whenever I listen to it, at first it sounds a little thin, kind of like it's lacking in body or slightly one-dimensional. But after a minute or two of adjustment my ears settle in. So that may sound like a criticism or that I don't like it - but quite the contrary, I keep going back because it has this fantastic clarity in the mids and treble. It's not bright, so much as just clear, and there's no sign of sibilance. In fact, it handles tracks with problematic treble better than the PEE51 I have here. It can also have a very interesting texture and timbre with things like toms and bass drums - it's quite punchy in the bass, and the sense of 3 dimensional space combined with tonality of toms makes drums rolls a treat.
So yes, it's kind of ... different. I struggle to think of another DAP or similar I've had that has quite the same tuning. PEE51 is much more of a full-bodied, euphonic type sound. I actually just picked up a Questyle M12 - which arrived today, so still pretty fresh - and that too has a fuller bodied sound than the Chronos, but is different again from the PEE51.
In all honesty, the three of them are all pretty impressive. I intend to only keep one - okay, maybe two

- and it's going to be pretty hard to pick a favorite. Amazing how far these tiny thumb-drive sized devices have come, and how close they get to replicating the sound quality of a reasonbly-priced DAP. In fact, I'm selling my PS and DX120; they do some things better than the dongles I have at hand, and I do prefer keeping music and phone separate, but when a dongle comes so close for so much cheaper, it's hard to justify keeping hold of them. So I think it's DAP days are over for me (for now). I'll use one of these paired with a desktop amp when at home, then unplug it and tail it to my phone for use on the go.