Cloudflare seems mature enough at this point that if you're willing to accept any kind of vendor lock-in, then accepting it through them is likely acceptable. I won't say they're on-par with the big cloud providers, but if they offer the services you need and you'd be willing to lock-in with AWS, etc., then they should be considered.

If you're generally opposed to any vendor lock-in, then Cloudflare is definitely a hard sell. Many of their services are pretty specific to their ecosystem and I imagine trying to keep things portable would be infeasible any many scenarios. Granted, this is true in a provider like AWS, too, if you were depending heavily on their proprietary, managed services. But there's definitely value in knowing that you can stick to "generic" services as much as possible in AWS and be able to move away relatively easily.

Cloudflare is definitely becoming a "real" cloud provider (I'd say their release of R2, for me, pushed them into the "serious contender" category), but they focus on pretty specific features that aren't very portable. This Cloudflare OS service is a good example of that. If it is exactly what you need, then it is worth checking out and taking on the risk of vendor lock-in. But if you're doing something where long-term planning and portability is important, then you'll have a hard time warranting even considering them.

Cloudflare OS does have the important risk-mitigating feature that you can fork it if the vendor becomes hostile to your interests. You can't really do that with managed services like Workers (workerd exists but isn't a drop-in replacement for the entire Workers platform).

Whether forking is economical depends, of course, on your scale and on how many others are in the same boat.