I have one. I built a control panel for it and hooked it up to my xbox at about 2am one night only to find that The Player 2 controls did not function at all.
I figured I was drunk by the time I got to the wiring part of the assembly and that I had somehow miswired something.
The next day I remembered that there were two connectors coming off the adapter, one for P1 and another for P2.
Even while drunk I can wire a control panel perfectly. I just cant plug it in right.

To answer your question, it works great. It works as advertised. I didnt even have to program the IPAC or anything. Using the default wiring and key mapping everything was where it was supposed to be.
Buy the little box for the connector, I think its like $3, (the case). It just makes the whole thing seem more professional.