We tried to use B2 for storing image and video files. First byte out is very slow (as expected). We however experienced bigger issues where if you try to upload millions of files per minute in their system, it crumbles. Huge amount of errors were thrown and their support could not help.
We decided to stick with king of storage AWS S3.
> if you try to upload millions of files per minute
may I suggest this might not be a typical usecase?
Yeah, :D But when someone hands over a storage system, temptation is high to store everything on it.