How you price is a conversion decision before it is a pricing decision
Flat rate and hourly billing produce different conversations, different objections and different close rates, and the choice is often inherited rather than made.
Flat rate quotes the job. The customer hears one number before work starts, knows what it costs regardless of how long it takes, and can compare it against another company. The objection tends to be the size of the number.
Time and materials quotes the process. The customer hears a rate, does not know the total, and is exposed to the risk of the job taking longer. The objection tends to be uncertainty, which for a nervous homeowner is often the harder one.
Most residential customers convert better on a known number, even a larger one, because the anxiety is about the unknown rather than the amount. Commercial and property management buyers frequently prefer the opposite, since they are managing many jobs and want to pay for actual time.
Whichever you use, the conversion work is in how it is explained. A flat rate presented without saying what is included invites the suspicion that it is padded. An hourly rate presented without an estimated range invites the fear of an open meter.
It is worth asking whether the model you use was chosen or simply arrived. Plenty of shops run one because that is how they started, and have never tested the other on the jobs where it might suit better.