an essential aspect of fixed hour contracts is that requirements need to be sorted from the most critical to the nice to have and the client needs to be prepare

an essential aspect of fixed hour contracts is that requirements need to be sorted from the most critical to the nice to have and the client needs to be prepared to drop the nice to have if the budget doesn't stretch to them which is the whole point of the agile manifesto which is why agile fails under most circumstances, as having fixed time, requirement and budget but under scrum and sprints is anything but agile.