Agreed. The fuzz 2 setting on the FZ 2 is more muff-like but I wouldn't recommend as a muff alternative.
You're thinking of the Boss FZ-2 which was based on a Superfuzz. The FZ-3 however is a Big Muff copy or at least similar.
I've have had an FZ3 and I don't remember it being muff-like at all, more a vintage fuzz type pedal like a tonebender or fuzz face. The tone control certainly didn't have the range of a muff. I currently have an FZ2 and the first fuzz mode is indeed similar to a super fuzz with a very noticeable octave in the sound but the second fuzz mode is a really scooped fuzz tone, similar to a muff but with a slight hint of octave in the sound - but nowhere near as much as mode 1.