Despite it's ongoing reputation, I honestly don't believe it to be a terrible "high gain" distortion/fuzz pedal.
I guess, because it was never my first pedal, nor have i paid attention to it in my early gear years. & having only really fx gear acquired from 2016 onwards. Having studied my 10 band EQ (& others for that matter), rethinking my tweak of the MXR Bass DI+ because its EQ shelving is far appart from each frequency, & as of recent having sat down with my swollen pickle fuzz & tweaked it to deliver what i wanted for fuzz on bass.
I understand where the "bad" tones from the metal zone can pop from, however there's a simple format to follow on how to tweak it to sound its optimal. It's a touchy EQ system, i'll admit which if you're looking to get a good sound directly, should consider being patient with the unit & themselves. My approach was starting with everything at noon (aside from the mids freq & level), leave the mid level around 1 oclock & shift the mids freq knob to where are satisfied with (given on guitar or bass the freq i wanted was different), then given that freq range, i'd either have it cut, or boosted. A good rule is if its in the low mids spectrum i'd have it cut (from minimum to about 10 oclock), if its in the high mids i could either cut or boost slightly (anywhere from 10 oclock to 1 oclock). Then i would tweak the Gain: if i wanted full blown fuzz, noon & above, or semi controlled distortion; noon & below. Then set the bass & treble, however i view them as resonance & presence to the overall tone - which makes the most sense, considering the treble can add too much fizz, & the bass adds more woofiness. Less is more in this case, let the mid frequency/mid level dictate the overall character, & let bass & treble be your accents.
I think its name is its bigger downfall. Yes it has sold millions, but no "pro" actually uses this on their board. Cause owning actual high gain amps & using "proper" dirt pedals like a ds1, or tube screamer if you're inclined to boost in such ways. If the metal zone was named/marketed differently, it might've faired more positively than the hate it gets. I guess just like the JCM900 dual reverb, coming after something which is highly praised (jcm800 in its case, vs the HM2 for BOSS), people expect a lot from the new comer which is suppose to be the successor. If the metal zone wasn't part of the "metal" family, & more on the "FZ" family of BOSS pedals, it would've been in better light. Not competing with its predecessor, rather being it'sown unique voice.
Truth be told, the zone kicks on bass (& guitar) in comparison to the ODB-3. It's EQ gives it a better edge, & i feel if i had an octave pedal before it, i'd pull off some weird chaos. It could probably cop some overdrive dirtiness by keeping its gain knob lower than 9 oclock. With its power EQ, it can give anything you'd seek character tone wise.
Easy to find on the used market for way less, if you're inclined, take your time with this pedal, & give it a chance to speak beyond the bashed hate it gets.