I've not tried it at 18v, kept meaning to but never got around to it. Anyone, by far the best overdrive pedal I've used and is very good value for money when compared to how much you'd have to spend on other 'boutique' pedals to get the same quality of sound.
Now, my Ampeg V4 driven really hard so the power valves provide the overdrive - that's the absolute tits, but in absence of this stupid loud rig then a BD works well