I'm not sure I get the point (besides using days for the estimation, which is a good practice). So in the end you are doing it on a fixed-price term, but you're

I'm not sure I get the point (besides using days for the estimation, which is a good practice). So in the end you are doing it on a fixed-price term, but you're stating a daily rate as well, for scope changes. (Which you'll still have to argue about, and you're still left with the estimation errors and the arguments about the specification errors.) Or did I miss something? (Or maybe there are a lot of people, who will not state a rate for the out-of-scope work and then they'll get into trouble when trying to ask money for that?)