Using the Electro-Harmonix Bassballs USA is very simple, as it only has a few parameters to control, and they're really the only ones you need on this as the pedal kind of does its thing by itself. The pedal has a large knob for setting the sensitivity, and a switch for adding a bit of distortion, and that's all you've got here. The sensitivity will make a big difference if you set it to three or nine o'clock. The distortion isn't all that heavy, but will definitely add some low overdrive to your sound. A manual isn't necessary unless you're having a technical problem, which it most likely won't be able to help you with anyway...
The Electro-Harmonix Bassballs USA is perfect for getting some simple, consistent, filtering going on in your bass rig. While I'm primarily a guitarist, I've played with a bass player who had this, and is definitely added a cool vibe whenever we would use it in this studio. I'm sure that it works very well with electric guitar as well, but like I said earlier I never tried it out so I can't say so fur sure. If you'd like some simple filter/wah type tones for your bass rig, the Baseballs is most likely what you're looking for.
Because the tone of the Electro-Harmonix Bassballs USA is so cool, I don't even mind having very little control over it. It isn't the sort of pedal that I would use all of the time, or even a fraction of the time, but when it does prove to useful it can really shine. The price is very reasonable, but they no longer make this version of the Baseballs, so you'll have to seek out a used one, which won't be hard to do. In general I'm not a big fan of effects on bass guitar, but the Electro-Harmonix Bassballs USA is definitely an exception.