This review was posted by David Gill (Montgomery Appliances) on the Haunting Mids forum. Since it was such a spontaneous and enthusiast review of 1 pedal builder about the creation of another builder (which he doesn't know personally), I wanted to share it here (with permission).
Been looking for an alternative to my B7K for bass dirt and after looking around and reading reviews it seems like the right choice was to stick with Darkglass since their pre/OD is so incredibly nice. IMO its an order of magnitude better than the other bass pres on the market. I ordered their Duality fuzz from Rogue Guitar Shop and it is the very best bass fuzz I have come across and actually maybe the best REALLY heavy guitar fuzz I've laid hands on in 15 years of playing.
I plugged it in with guitar in Drop C before plugging in a bass and was floored. Most bass fuzzes don't sound great with guitar. The B:Assmaster is a good case. Sounds splatty and cool with bass but turns notes into mush and nothing much else with guitar. I thought the TAFM was killer with bass and did a really great low gain guitar fuzz, but at higher levels of gain it felt a little atonal. That was the very first version and I believe they are different now. But the Duality is just a massively bass-heavy wall of fuzz with the blend control all the way wet and blending in a little bit of dry even still sounds good. Usually that's pretty ugly with guitar. No gain control so its probably at max for the circuit which is a TON of gain, yet when you stop playing its not extremely noisy like a muff. It cleans up a bit with your volume knob and the filter control is perfect for setting the right amount of edge and pick definition.
Duality control goes between a splatty fuzz on the left and a smoother more modern sound on the right. Its like two voices in the same theme. The overall sound is really like every fuzz I like mixed together. It has the gain and texture of a muff, but more smoothness and attack like a foxx tone machine. And then it has a bit of the gated quality of a fuzz factory and some of the character of a buzzaround.
With bass its equally thick and huge but without the large grain of a B:Assmaster or even a muff. The gain structure of very fine and smooth and clean so it sounds more like a guitar distortion than a bass distortion, while still holding down all the bass power and hugeness.
I'd pretty much recommend it to anyone who wants a heavy sounding fuzz and doesn't just want another muff. The twist ending is that this pedal could be entirely muff based but I haven't poked around inside. If dude can design a great bass pre though I kind of doubt he just plopped a clean blend on a muff and called it a day.