Absolutely, I'm not sure about the poster's intent, but his concerns still apply to using it for developer testing

If your application uses features that don't work in LocalStack, it can be very tricky to start using LocalStack to test that application. Conversely, if you are already using LocalStack to test/develop your application, that may discourage you from using AWS features which might be a good fit, but aren't supported by LocalStack.

Also, I would certainly recommend against solely testing with LocalStack, since you may run into situations where it behaves slightly differently than AWS, and if you develop targeting LocalStack's behavior, you could end up with bugs when AWS behaves differently in production.