This is basically a really good clone of the Boss HM-2 "Heavy Metal" pedal from the 80s which made a sound popularized by bands like Dismember and Entombed - what became known as "the Swedish sound" in death metal circles.
It's pretty much the same as that pedal, even the "distortion" knob behaves in the same way (pretty much no change from 9 o'clock to 4 o'clock then all of a sudden BANG !
Don't be fooled into thinking this is just for "heavy metal" as in all honesty it's not really that useful for getting that sound, there are better pedals, but if you're looking for really meaty distortion for the more extreme end of the metal spectrum then this is a great pedal. It's not as distorted as the MT-2 (Boss "Metal Zone") pedal but that pedal is, imo, REALLY overrated and very hard to get a good tone out of, far too much high end and in a live situation it really doesn't cut through the mix.
If you're looking for serious, "buzzsaw" style distortion then this pedal will definitely hit the mark and the difference in sound (very little) doesn't justify the inflated ebay prices that the HM-2 is fetching these days, especially the Japanese version (which is the most sought after due to apparently having the most 'Swedish' sound). The knobs on this pedal truly do replicate almost exactly the sound/useability of the pedal it's setting out to copy. I've not taken it apart so I can't say if they've copied the circuitry exactly but, knowing Behringer, I'd imagine it's as close as they can get it with modern parts.
The build is, as usual for the Behringer pedal range, good quality BUT the pedal itself IS hard impact plastic (Just letting you all know incase you're expecting a metal chassis). This isn't a problem and unless you're jumping up and down on it very hard you will get a long life out of it and it's more than useable in a gig situation, contrary to what some purists (idiots?) might say about the range. For this price you can't really go wrong.
Coincidentally, I have both the Taiwanese and Japanese versions of the HM-2 and I really would say there's very little difference between those and this pedal. I bought this as it was only £15 just to see how it sounded, I was curious as much as anything else, and will now probably gift it to someone who is looking for an HM-2.