This compressor sounds great and has features you would not find in other compressors of its price class. It lets you adjust all common parameters such as attack, release, threshold, and also provides a sidechannel send/return which can be used to e.g. change the frequency response of the compressor or to send in an external signal (such as a bass drum track).
I really like the sturdy box, the above features, as well as the humorous and honest manual (download only).
Unfortunately, this compressor was not a good choice for my instrument, the Chapman Stick. While the compressor works on a stereo signal, it does not have separate controls for each channel. For the Stick this means that the bass strings are heavily compressed while the melody strings aren't. It was hard to figure out a good balance. Using an equalizer on the sidechannel signal may have been an option, but I eventually gave up.
I would recommend this compressor for mastering.