It is a really subtle but useful change. It doesn't change the signature in the sense I think many of you are perhaps thinking. If you listened to an original Alpha Dog production vs new, what you'd hear tonally is that the highs are simply better integrated, smoother and more balanced. It is technically fairly close to reducing 4.3 and 8.6K by about 2 dB, but it does a bit more.
Because of the physics of what the dot is doing to reduce those peaks it enhances the sound in a couple of other ways, as well; increasing the sense of dark space and improving soundstage and imaging.
The felt discs are there for people who may prefer a slightly darker overall tonal balance. One makes a minor shift, two makes it fairly dramatic, too much so for me but some people like that darker tone. If you have paired with really bright sources, for example, or if you are just one of the people who wants a top end "soft" of neutral they are available.
One dot with one disc can sound pretty nice on some phones. I liken it to tube rolling on the Lyr or Liquid Glass. It doesn't become a new amp, but you can dial it in.
P.S. check out www.hometheaterreview.com today