Good point, but I have found that just doing it right the first time works for me. In fact, I'm doing it right now. In the Xcode window, I'm building a test release that the team will run and review for usability issues and bugs.
If they find any bugs or issues, I fix/address them before moving on to the next function implementation.
The significant advantage that this confers, is that the app is constantly in "release-ready" form; although incomplete.
Useful, for when we want to ask people to give us money. We just get an NDA, loop them into the TestFlight group, and let them have at it. No need for chaperones from Marketing, or sacrifices to the demo gods.