Yeah, it is a Gameshark like thing.
I have been unable to get it to work with the M3, so I cannot answer your other questions. (Note: I have not tried very hard to get it to work. The documentation is lacking, and you cannot get a straight answer from anyone on how to get it working. No one seems have a solid way to get it working. But, if you look around, you will find millions of ways to install it.)
It appears though that the M3 software has it built in, I just do not know how to use it. But from what I gather, you get codes from "somewhere", past them into the text files of the m3 game manager, then upload the game. Note that this is all theory.
Note that I have researched this subject quite a bit, but there are so many different theories/ideas on how to get it to work that I became confused and just gave up. (There are not many/any games that I would use it for, so the drive to figure it out was not really there.)