OpenAI and Anthropic steal my money by expiring unused API credits, which is illegal in my country. OpenRouter also has a clause to do that in their terms of service (although they haven't yet, and some employee on their discord assured me they won't). Not sure about Eden AI (they have some fishy stuff in their ToS like "Unless otherwise stated, payments are non-refundable"), but at least I could sue them without buying an international plane ticket if the need arises.

But the most important advantage is the convenience of being able to try out new models without subscribing to yet another service.