Use of the Services for serving video or a disproportionate percentage of pictures, audio files, or other non-HTML content is prohibited, unless purchased separately as part of a Paid Service or expressly allowed under our Supplemental Terms for a specific Service. [1]
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[1] 2.8 Limitation on Serving Non-HTML Content https://www.cloudflare.com/terms/
See: https://www.cloudflare.com/supplemental-terms/ § Cloudflare Pages and Cloudflare Workers®
The said limitation should apply however to their tranditional service with orange on whether it is B2 or not. I am not sure if being a Bandwidth Alliance partner makes a difference.
If R2 can be approximately as reliable on ingest as AWS/GCS/Azure is, but without the egress fees of the other major providers, then $0.015/GB-month seems like a pretty good deal.
Backblaze, DO Spaces simply were not designed for this in the first place.