This optical comp pedal comes from a boutique company in Poland. Each of their pedals comes in Black or Silver models, where the Silver version has added features and fancier cosmetics; this review is of the Black one.
 
It has four knobs: "Compression" which controls the threshold; "Level" which controls the output volume; "Punch" which controls the attack time; and "Range" which controls the frequency range of your signal that triggers the compression. That one is a little tricky to explain. The knob goes from "narrow" to "wide"; at the wide end, the compression is triggered by your whole frequency range, and as you turn the knob toward "narrow", it reduces the range downward from the high end. So turning it down a little bit means your highs are not triggering the compression, and turning it down a bit more means the highs and the mids are not triggering it, and at the narrowest end only your lowest frequencies trigger it. It's a sidechain system, similar to the ones in the FEA OptiFET and the Daring Audio Phat Beam, although those two have more controls over the sidechain. This is a really great way to get back some of the articulation that can be lost when your signal gets heavily compressed.
 
When you combine a medium "Range" with medium "Punch" (attack), you can get a really crisp, percussive effect. This becomes even more dramatic if you lower the threshold, so that the low frequencies cause heavy squashing while the highs stay snappy. That more exaggerated end might not be an effect you'd use all the time, but it's very cool and very usable, and at less extreme settings it just offers a more articulate sound. Quite likable.
 
The tone in general is neutral and clean, with no loss of highs or lows. It doesn't add significant "fatness", but adjusting the frequency range can bring out a more lively full tone. The action is smooth, with a bit of dip and swell at the heaviest settings.