Extensive compressor reviews and FAQ

Strymon OB-1: This is an optical comp pedal with an added clean-boost function. The compression is very simple, with only two knobs. The action has the smooth, natural quality typical of opto comps.
Its "Comp" knob appears to control the ratio, from 1:1 to very strong, perhaps 20:1; but while it can do some peak limiting at the highest setting, that's not where it sounds or works best. Overall it does best in the light-to-medium range, adding a bit of fatness and sustain rather than heavy squashing or noticeable "effect". There is very little noise, even at the high end of the Comp knob.
The tone is clear and uncolored--maybe not quite as transparent as the Rothwell, but close. It loses a bit of the low end, about the same as the Ross/Dyna/Keeley types, but it does not lose any highs. Strymon offers a "bass mod" now, that was not advertised at the time of this review, and I have not tested that version yet.
The clean boost is exactly that, but with one tweak: it has a 3-position switch allowing boost of only the highs, only the mids, or the full-range signal. It has its own level knob and footswitch. The boost is bypassed by the main bypass footswitch, so it will not operate separately from the compressor. Also, the boost comes after the compressor, so hitting the boost does not change the amount of compression.
The housing is a slick-looking custom metal design, slightly larger than the Diamond and Barber "medium" standard. The construction quality is quite nice, and the footswitch is "true bypass". It runs on standard Boss-type 9V DC.
I know this review seems awfully short and terse, but there's really not much to say about this pedal. It's clean, it sounds good at moderate settings, it has low noise, the boost may be useful to some people, and the standard model is not great for bass due to losing a bit of low end. That's about it.