we're building bug0 on exactly this model. our managed testing service charges a flat monthly fee with a dedicated sdet assigned to the customer. the outcome is clear: regression coverage that works. not hours logged.
what i've seen firsthand: outcome-based forces you to be opinionated about scope upfront. if you're vague about what "done" looks like, you eat the cost, not the customer. that's healthy pressure. keeps you from overengineering.
the risk is real though. some customers keep expanding what they expect within the same price. you need tight boundaries or you're doing 2x the work for the same revenue. we solve that with async slack channels where scope stays visible and documented.
hourly billing rewards inefficiency. outcome-based rewards clarity. pick your problem.