I can really think of no good arguments against Flat Rate Pricing as it relates to service work. One huge advantage is all your technicians become estimators. They have a book they can reference and give prices in the field.
Let's face facts, running an electrical contracting business has become so expensive, the average residential customer would freak out if you told them your hourly rate, it's better to deliver a flat rate price and avoid shocking the customer.
Auto mechanics use flat rate pricing. They're probably getting $90+ an hour but know that consumers will balk at paying a "grease monkey" such a lofty sum. Consumers are incapable of understanding how business works, that's why they're employees.