There isn't much to using the Radial Engineering ProDI at all as everything should be able to decipher without the assistance of a manual. Simply make your connections and you're good to go. The ground lift and pad both come in handy more often than not, so it is certainly nice to have these features. Beyond this, there isn't much to know about make up of the ProDI.
As far as stand alone direct input boxes go, the Radial Engineering ProDI is one of the better models that I have experience with. I've used it to record bass guitar, in tandem with a mic'd up bass amplifier. Bass guitar is probably the most recorded instrument through a DI box, but this would definitely work well for getting any sort of direct signal, as it will reproduce your signal accurately and faithfully without adding any sound or noise of its own.
When it comes to DI boxes, Radial Engineering is one of if not the best in the business, and the ProDI is one of their best and most affordable models. Suitable for both professional and home studio owners looking for a DI box, the ProDI is a great investment that will last a lifetime as it is built like a brick! Highly recommended for studio owners of any kind...