Author here. AWS is quite a bit more expensive than cloudflare, mostly because of egress charges from Cloudfront.

Cloudflare R2 latency is tricky to predict and can be anywhere from a few hundred milliseconds to 1s+ in my experience. This is for cache misses, only, of course; cache hits are comparable to AWS. Cloudflare really has every incentive to improve their product so I expect this to be much more competitive in the near future.