Using the Great River MP-500NV is quite simple and won't present any problems for those who have experience with mic pres. It simply has two knobs - one for gain and one for output cal in addition to buttons for polarity, phantom power, impedance, and loading. Beyond this there isn't anything that you need to know about the MP-500NV in terms of configuration, so I don't think that a manual is really necessary.
The tone of the Great River MP-500NV is overall really great. I love recording everything from vocals to drums through this as it has a fat tone that is perfect for getting a clean yet full bodied sound. It is also a great sounding direct input box in general as it is just about as good as a DI box as any I have used. While this isn't the most versatile mic pre in terms of parameters and knobs to play with, I find that the simplistic nature of the pre helps me to get a quick sound without having to worry about too many controls.
In my opinion, Great River is one of the best in the business when it comes to mic pres and the Great River MP-500NV falls right in line with their best gear. Obviously this doesn't offer up the same features as some of their higher end outboard gear, if you are on a budget and looking for a great mic pre/DI box, there is no way that you can go wrong with the MP-500NV as it simply has a great tone quality. While this might be too expensive for most home studio owners, it is still very reasonably priced for such a good sounding mic pre and I would highly recommend it for anyone looking in this market.