The reason it’s a mediocre implementation would be obvious if you (or really anybody here) had bothered to read detailed measurements of other PuriFi implementations, which routinely reach -120db SINAD.
That's why it's nice to put supporting evidence or points in your post at the time you throw shade. It's far to easy to misinterpret any particular reason why you felt this was mediocre, or to be unable to seek out possible disagreements in the interpretation.
The actual specifications are:
>120 dB (A-weighted, ref. 200 W out in 8 ohms)
So, you are incorrect, by 6 dB ( a lot) at 1 watt and please be sure you are measuring apples to apples and using the correct power spec for the S/N. If not specified, assume it's at full power.
I strongly suspect your 120 dB comparison was at full power. Let me know if you find a reference to data that shows my interpretations are mistaken.
Best,
Erik