I bought the Meatbox to use on guitar, bass, and most probably on bass heavy instruments like bass drum or organ cab (with a mic and and impedance transformer).
The sound : At first, I wasn't impressed on guitar, but it gets massive when you put the Meatbox into a fuzz (Big Muff Bass for me) you can get some heavy blasting tones with that combination. Great for a stoner sound.
Alone on electric bass, it's far more interesting than the guitar (duh !) and you can get some really deep tone. But again this effect reveals more of itself with saturation afterward.
The controls : apart from being a reported speaker blaster, this pedal is known for its rather not-intuitive controls. The manual stands that the SUB and LOW knobs can boost or cut, so a good starting position would be with these two set on 12 o'clock, OCTAVE on zero and volume at full blast (this pedal severely lack of headroom as the output drops significantly the more you push the controls). With the OCTAVE knob at maximum you get the added signal only, with can be very cool.
The tracking : for those who wonder, yes it's polyphonic. The tracking is better on the lower strings, both on guitar and bass. It doesn't track super well neither (it really depends on your settings, and what material and level you feed it with), you can hear the tracking switching on and off when a string resonates with another, or even on a single string. Maybe the trick would be to feed it with a boosted signal, didn't tried yet. But overall it's totally playable if you don't mind some kind of glitches in your sound… which is part of the fun, at a certain extend !
The hardware : the enclosure is full metal with a flat plastic backplate (sticker rubber feet provided). The 9V battery snap cable is so short you can barely fit the battery on without ripping it, it's a shame. The blue LED is very agressive, thinking of switching it. Some might like it tho. The ON/OFF switch feels kinda cheap, as the knobs. Overall the construction is ok, but a little pricey for what it is.
Conclusion : There are only a few competitors in that niche, and overall the Meatbox is a good sub-octaver with enough parameters to sculpt the sound, which can get absolutely massive, despite my first impressions. You'll get the best out of it conjunctly with some kind of saturation, and it takes time to get used to the inter-dependants controls. The extra DRY output is a great bonus.