The make up of the Diamond Pedal Compressor is just about as simple as it gets for a guitar pedal. You've only got three parameters - compression, EQ (tone), and volume, so even if you have minimal experience working with compressors, I think you'll be able to catch on to everything going on here rather quickly. Beyond the three major parameters there really isn't anything else to take into consideration, so I don't believe that a manual is necessary unless you are having some sort of technical difficulty.
While I can't say that the Diamond Pedal Compressor is my favorite compression pedal in the world, it definitely has an overall great tone. I've used a lot of different compression pedals out there, and this is one of the better models that I've used. I've only used the pedal with electric guitar - usually a Fender Strat or Jazzmaster and a '76 Fender Twin Reverb, and I find I'm able to get the types of sounds that I want within this configuration. The compression tone can be described as punchy and clean, although I do wish that I would be able to get more varying types of tones with this pedal...
For me, the only problem with the Diamond Pedal Compressor is the price. While it is a very good sounding compressor, I have found some similar sounding compression pedals for half of the price like the MXR Dyna Comp for example. This isn't to say that this isn't a great sounding compression pedal and that it won't get the job done in most situations, it's just that I wish it was a bit less expensive. Having said that, if you're looking for a great sounding compression pedal, this one should definitely be in the conversation as not considering the price it is a great pedal.