I have the CanCan. Using my poor ears, here is what I hear.
Factory Notos: Ping, Huh-woof,Projectile impact (could be Huh-Woosh)
With CanCan: Ping,ffFt,Projectile impact
This is like the proverbial Hollywood 'ffFt', only quieter and much lower in pitch. for sure the 'Huh' is blunted by the CanCan, regardless of what sound follows after. Definitely quieter shot noise, but not 10 dB quieter to my ear, more like a few dB reduction. Honestly, the Notos is pretty quiet already, I have airsoft and CO2 guns that are noisier even without the addition of the CanCan. My Tatsu moderated Avenger (40 FPE) is quite a bit louder than the factory Notos. 'Ping' and 'Projectile impact' are unchanged, neither are likely to be changed by any moderator.
I have put open-cell foam in the CanCan volume and it does quiet it a teensy bit more.
One thing I did not expect is that the look has grown on me strongly. The front end of the Notos looks anemic to me now without the CanCan.
The noise reduction with the CanCan is certainly worthwhile to me for backyard shooting or urban pesting/hunting, but I value quiet way more than I ever thought I would.