Easiest way to tell whether it's worth it or not is to run some back of the envelope math on how much it'll cost to build and run (dev time + infra costs) vs relying on 3rd party.
5-10k seems like a low enough volume for 3rd party to be a good idea.
When you get to the high hundred thousands (let alone millions or tens of millions) it becomes prohibitively expensive to not roll in your own system.
