The Visual Sound Comp 66 is a compression pedal that is suitable for any electronic instrument, but I'm sure is primarily used for electric guitar, and that is what I've used it for. It is an analog pedal that has 1/4" connections for input and output and requires standard nine volt power. It isn't rack mountable in any way as it is a stomp box.
Using the Visual Sound Comp 66 is a very simple process. Even those who don't have much experience with compression in the past will be able to figure this one out fairly quickly. It's just got parameters for compression, tone, and gain, really making it as simple of a compression pedal as you can make it. You can even switch on or off the tone knob with a switch if you'd like. I don't think that the assistance of a manual is necessary at all with the Comp 66.
Even though the Visual Sound Comp 66 wouldn't be my first choice for a compression pedal in terms of a pedal to use for electric guitar, it definitely has a very respectable sound. It is capable of giving you a very squeezed tone as well as a more subtle sound for just getting some more sustain. I've really only tried out the pedal and haven't done any recording or performing with. I was using it with a Fender Stratocaster and a Marshall combo amplifier. In my limited experience with the pedal, I definitely felt I was able to get a few different nice sounding tones with it.
While I definitely like the way the Visual Sound Comp 66 sounds, there are a few pedals out there that I'd definitely rather use like the Boss CS-3 and the MXR Dyna Comp. There are a number more that I could mention, but they are more expensive so I think I should stick to comparing it to pedal in it's price range. Unless you're spending more than $100 USD on a higher end pedal, I think you'll find that the Visual Sound Comp 66 is right in the range of most of the other compression guitar pedals out there, so price won't be much a factor. I'd definitely suggest that you try out the Visual Sound Comp 66 in addition to pedals like MXR Dyna Comp to see what will work best for you and the sound you're going for.