This is a very usefull pedal, which can do from light compression to strong limiting. With all those knobs, it can look intimidating for those new to the compression world, but a quick look at the manual and at the ever usefull www.ovnilab.com should put you on the right track in few minutes.
The adjustability of the attack & release time are extremely usefull to retain (or get rid of, if that's what you are for) the initial spike of each note. One important thing to note is that, even in the slowest settings, the attack is still quite (very) fast. This is not a problem for me, but it may be for others.
Even if the compression ratio is not infinitely adjustable, the four offered ratios have been thoughtfully chosen and so far I have not missed further adjustavility.
Last but not least, I really hope that whoever thought about including that gain-reduction status LED meter got a considerable rise on his/her payroll. It's pure genious! For an effect so difficult to adjust just by ear as compression, that extra visual confirmation of what's going on really eases things. Well done!