Brilliant.
I got one cheap locally.
I like it. It does exactly what EHX says it does. It mainly cuts bass, and also boosts treble. Yes, the bass cut is quite extreme. But it is outstanding to clear up a heavily saturated amp so you can still have the saturation, but with clarity.
At cleaner settings, it just gives you a classic "lo-fi" tone. Sounds like playing a guitar through a boom box.
There is a cap mod that a guy on You Tube posted. I might try that and might not. I'm quite happy with what it does when the amp is dimed and I don't want to lose that.