In my opinion, unit tests are great as a scaffold while building something. I'm not sure how much they help after that. If the behavior that they're testing can be pulled up into the integration test, then that might be better, which would leave more room for refactoring the implementation (although pulling them up too early might be a waste if you don't feel the need to refactor the implementation).
So my stance at this point is: write unit tests, but don't get too attached to them.
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