Bloody well-made, first impression.
Plugging it in, I feel like Im 15 again learning Black Sabbath riffs. It speaks to my musical DNA.
I really like that it is better at lower gain than other Muffs, the aggression is somehow more nuanced at that level.
Its not easy to use with an amp live, in a real context. You may struggle to integrate it with your setup. Its easier to build up the right guitar/pedals/amp setup around this thing than just fitting it in.
For bass its easier as an "always on" base tone than turning it on and off, as its tricky getting the tone to sit well in contrast. But yes for bass its ridiculously good fun.
It is what it is, and if you like that, you need this. Even if you have other Muffs, you may want to try this one out.