I haven't used it so just spit balling, but surely it depends on the quality of the review? If it picks up lots of issues and prevents downtime then it could work out as worthwhile. What would it cost an engineer with deep knowledge of the codebase to do a similar job? You could spend an hour really digging into a PR, poking around, testing stuff out etc. Im guessing most engineers are paid more than $15-25/hr, not to mention the opportunity cost.