Can it really get any simpler than a two knob pedal? Well, that's what you're getting with this Keeley Compressor. There is also a four knob version, but from what I've been told this one is all you'll need, although I've yet to use the four knob version myself. This one has knobs for just sustain and output level, which is about as basic as you'll find a pedal. A manual shouldn't be necessary since it's so simple.
Hands down the Keeley Compressor is the best compressor that I've used for electric guitar. It really can make your guitar sing, as the sustain is perfect on this bad boy. I've used it within a few different set ups and with a few different players and it always seems to get the job done with it's milky smooth sound. I don't own this pedal, but if I were to upgrade to one pedal in my rig it would definitely be this one! It's hard to say exactly what sets it apart from the rest, but one listen to it and you'll know exactly what I'm talking about...
If you want the best guitar pedal compressor that you can buy, look no further than the Robert Keeley Electronics 2 Knob Compressor. It's simply that good. The price isn't going to be cheap, but when you consider that you're only spending a bit more than you would for another compression pedal, it seems like it would be worth it in the long run if you're able to do it. I don't own one of these yet, but I'm definitely hoping to get one soon!