It's a genuine ad. I have two Phasure NOS1 DACs here myself, neither of which I now use, since going fully active a few years ago. I don't know the seller personally (though we happen to live in the same town!), but I was aware of him when I was active on the Phasure forum (quite a few years ago now).
The asking price, for a DAC with 8x genuine PCM1704U-K (highest spec) chips, is reasonable, I think. But...
1. It's a NOS DAC and has no internal filtering whatsoever. However, unlike most other NOS DACs out there, it accepts 24/384 (or 24/768 if using the Phasure software player), so you need to upsample 8x or 16x to get the best out of it. Roon does this very well.
2. Sigma-delta DACs have come on a long way since this Phasure DAC was introduced (12-13 years ago now, though there have been a couple of updates along the way).
My Phasure DACs have the USB filter too, but I prefer the sound bypassing it.
Would I be inclined to take a punt on this one myself? Maybe, if...
1. I was looking for a 2-channel DAC
2. I wasn't satisfied with the sound of any sigma-delta DAC I'd heard to date
3. I was interested in hearing what a good NOS DAC can sound like
4. I was pretty good with a Windows PC (required)
5. I didn't already have two myself!
Mani.