I am in a lucky position to have Diezel amp, the D-Moll (mini-Herbert) and I have to say that this pedal really does sound like the pre-amp of the Diezel amp.
This pedal going into my Two-notes CAB-M gives me the perfect late night silent high gain recording sound, without annoying the neighbourhood, which sadly my real Diezel set-up does. It has the Diezel mid removal sound which is switchable to give you 'that sound' (which is why you buy the pedal).
Yes it is a relatively expensive pedal, and it is a BIG pedal. I dropped two stars on the fact that you need a relatively high miliamp 12V supply to power the thing, so your standard 9v power block won't power it (unless you have 12v outputs also), which is a bit of a pain.
The presence and deep control allow you to really tweak it you your amplifier - even my Peavey Bandit. What is nice is that it has a specific output to put into the effects return of your amp or into a power amp to be a self contained proper pre-amp.
KILLER sound though! (very different to Engl, Marshall or Peavey). So very happy with it..