I bought this compressor following a lot of research and listening to different comparison videos, to make my own opinion, based on what I hear. This thing sounds incredible on male vocals, guitars, synths and sources that need gentle average opto compression as well as benefit from the harmonic distortion imparted by the tubes.
Just like with original, its 'sweet spot' is somewhere in the region of 7-10dB GR, but unlike with plugins, this much compression does not destroy the signal in any way, but it sounds natural and smooth. The gain knob is where you can add the tube distortion to the signal. When you push the gain, it starts to distort characteristically for tubes, but again unlike with plugin emulation, it's a round and pleasant kind of distortion that may be used for artistic effect as well. I believe that the distortion occurs only once gain is pushed beyond normal signal level. Normal operation results in very clean and smooth signal with a litle bit of tube thickening. It does make source audio sound more like a record instantly. When applied to guitar tracks with amp simulation, it compliments tracks with tube harmonics, and removes the digital harshness and sterility. It's subtle magic box!
Obviously it outperforms plugins, and I believe tube distortion / saturation is one of the hardest to emulate on PC. Once you run this, you can instantly feel the difference. Such is my experience with quality analog equipment - it's not always obviously heard, but definitely 'felt', particularly when layered in the mix. The trick is to be subtle and to layer multiple layers in your mix. I also recommend this for tracking vocals, to control louder passages.
At the price slightly higher than plugins, it's LA2A clone hard to beat, but one that brings in pro studio sound to your mixes