Hi, I'm the author of Que. It's true that you can't really completely solve the idempotence problem for jobs that write to external web services (unless those web services provide ways for you to check whether you've already performed a write - see the guide to writing reliable jobs in the /docs directory), but that's a limitation that'll apply to any queuing system. I'd definitely say that Que, being transactional and backed by Postgres' durability guarantees, does give you better tooling for writing reliable jobs than a Redis-backed queue would in general.
I'm happy to answer any questions you or anyone else might have.