The ZEN is unique. The construction is based on the legendary compressors used in Abbey Road Studios. It's the musical canon of art used by The Beatles. The ZEN Compressor audio circuit is based on 14 bi-polar transistors in each channel. The compression is achieved by 8 hand-matched Zener diodes biased by a perfect feedback circuit.
ALAS, there is a dent in the unit in the back. I purchased it used (barely used, they said!) and never noticed this until now. I am chagrined. Because of the dent, the price is low. I have used the unit, and loved it. But I upgraded to the more expensive Chandler Zener Diode Compressor, which is very similar, but which I like a bit more, and I can't justify keeping both.
You can see the dent in the photograph of the back of the unit, along the bottom edge.
I'll warranty the compressor for 30 days so you can have ample time to make sure it's all good for you.