I run the HM-3 through this setup [in order]:
[friend's] Peavey Raptor EXP Plus
Boss HM-3 Hyper Metal
Ibanez CF7 Chorus/Flange [used for lush chorus]
Vox Wah [vintage][used as a filter]
Dunlop Mr. Crybaby [volume/wah]
Ibanez PM7 Phase Modulator [used for synth-like noises]
Crate GT212 120-Watt Combo [all mids cut]
It is noisy - a little background hum - but this is probably due to the fact that I use it with either cheap or old, beat up guitars. I haven't tried it yet with something with Duncans or EMG's - THEN, it might not have the hum.
This particular unit's namesake - Hyper Metal - coerces the thought that it's a face-melting, high-gain, in-your-face distortion unit. It isn't. It's merely a really awesome chunky, bass-heavy driver, but that doesn't make it bad. I've had this thing for about half a year now, and I've found great tones out of it - everything from a Hendrix-esque Octavia-like octave fuzz [with the gain at about 9 o'clock, the highs at about 3 o'clock, and the lows at full] to a more-than-decent thunderous "scooped" crunch [gain at full, highs at 12 o'clock, lows at full to 3 o'clock]. It's not really "scooped", because you can't cut the mids, but when you cut the highs, it sounds similar, and it makes me happy. Makes my 120-watter shake with a little palm-muting. :)
If I could relate this thing's sounds to any artists today, it'd have to be Jimi Hendrix, Tommy Iomi, and [strange but true] Darrell Abbott. I say Darrell because when I mix my amp's Rhythm [overdrive] channel with the HM-3 and an undisclosed "special pedal", I can get the exact same tone to the solo of the Pantera song "Walk" - the thick, bluesy smooth thrust. Very cool.
The HM-3 works great with a lush chorus effect, as well as a flange, although my flange is pretty shoddy. With a phaser, it gets pretty metal, and my friends, as well as I, love the unique tone that this thing puts out, especially through my amp's tube-emulation circuit.
You have to be fairly tough when you step on a Boss pedal - you can't just brush your foot on it, and it will turn on, like my Ibanez pedals. It pisses me off, especially during practice, live, and recording sessions. Gotta stomp on it - it's a friggen stomp box.
I would use this without a backup, but not as my main distortion. I hunger for a high-gain crunch, e.g. MT-2, Digitech Metal Master, Randall Warhead, etc. I would, however, use this unit for fillers, intros, and that sort of thing, just to mix things up a bit.
I like it.
I play anything from ambient soundscapes to disco to funk to blues to polka to high-gain-grandma-killing-bass-heavy crunch metal and beyond. This works for most of my styles.
In the instance that this were stolen or lost, I would try to get it back, or get something of much higher gain, like the MT-2, Metal Master, etc. It's a unique unit, and due to the fact that THEY DON'T MANUFACTURE THIS ONE ANY LONGER, I'm keepin' it.
One thing I wish this had would be a mid control. That's about it.
Remember, kids - this is more of a crunchy, high-gain overdrive and not a high-gain distortion. You can barely get pinch harmonics out of it, but hey - works for me.