Hetzner Storage Box is not even remotely a similar product to B2, considering the only reliability offered is the disks being in RAID. There is no geo-redundancy at all. The number of simultaneous connections is also quite limited, though this might not matter for many use cases.

I feel what you need to chose between $5/m and 99.999% SLA

B2 has no geo-redundacy by default. It's RAID across a bunch of neighboring servers.