I've seen productivity gains from unit testing and no gains when adding TDD to a process and team already invested in unit testing. Anecdotally, in my experien

I've seen productivity gains from unit testing and no gains when adding TDD to a process and team already invested in unit testing. Anecdotally, in my experience TDD crystallizes sub-optimal implementations early on, especially for junior developers. Unit testing allows fearless refactoring but TDD makes developers less likely to refactor in the early stages where it's most beneficial. Gains from code reviews are hard to quantify because people code differently when they know they are being code reviewed. Most of the gains come from simply announcing that code will be formally peer reviewed. Critical bugs can cost 100x to fix since the out of band release costs can be so high. Non-critical bugs just get added to the next sprint and the extra cost is in the support costs, if any.