There are techs who thrive under the pressure of flat rate, but most either don’t (making too many mistakes) or they feel that the flat rate system has burned them too much.
Too often management uses flat rate as a way to control their labor expense (which is exactly the wrong way to look at technician time, they are a commodity not an expense) instead of trying to create ways to make the technicians more efficient.
I personally think a hybrid pay system is best as it rewards both quality and speed.
Sorry if I ramble a bit.