This is exactly why we need this PreANN topic, to show the basic idea and collect feedback on it and on our presentation of it. So thanks!
Now to your questions. Why is it useful? Well, until we get the real immortality, digital one is the next best thing. And it is also like a plan B, just in case. Or a plan C after Cryonics. It is better to save yourself at least in detailed digital form, than not to do this at all.
Can a person fake his character? Yes, indeed, but that's his own choice. He may want to store the "real" self, as close to actual personality as possible, or he may decide to adjust some stuff, to "forget" what he doesn't want to remember and so on. Yes, this kind of kills the idea but everyone should be free to choose for themselves.