I wish there was a "dual function" switch so it'd be easy to A/B it. Honestly, I probably wouldn't have even known how much better I'd like the sound if I hadn't first heard it with the circuit out of the picture, which was due to a minor wiring fault at the time I rec'd the bass (as I posted before). Kinda' like not knowing what you're missing, so to speak.
With it "back in" after fixing the wiring problem, I found I especially didn't like it turned all the way down (a bit dull sounding), but the diff between around midway and all the way up (brightest) just seemed to be varying grades of non-optimal... some stuff gets better, but other stuff seems to suffer. Just couldn't find a sweet spot that I thought compared to the sound I had before. Not sure how to quantify it better. Just not a good high end profile in general IMHO... at least compared to a straight wired bart pre. It just seemed to open up the sound and fill in some "tonal holes" when I took that darn thing out.
All this said, I also realize this is ALL personal pref. But I would find it VERY interesting if someone else were to explore this a bit and see if they agree or disagree with me (no problem either way!!!). If done carefully, there's enough wire that it could be reversed and the Sparkle circuit returned to active duty if desired.
FWIW anyway.