The Haztron III+ is a very good filter...just not quite as quacky as the original. Someone needs to post samples of MuIII & Haztron and see it if anyone can pick out what's what.
It is very good indeed! better than Qtron+ or FM4 imho but sounds "thinner" than the proton (sorry for lack of better words... maybe a different filter slope or speed of envelop?), is huge, heavy, not compatible with standard 9v boss power supply, and has these big pads underneath (yeah I never tried to pull these out) that make it difficult to scratch on a pedalboard. I have some volume drop with mine also... never tried an original Mutron III+.