Keeping questions from scale & benchmarks aside, this is a cool thing for functional/unit testing module that uses SQS, instead of dumb mocks.

Thank you! Yes, you should definitely use this instead of localstack :)

Although I wouldn't recommend using LocalStack's SQS implementation for production workloads, calling it a dumb mock is a bit outdated. It emulates pretty much every SQS behvaior including long polling, delayed messages, visibility timeouts, DLQ redrive, batch send/receive, ...