Although if you happen to be within the target audience for their business model (like I am) then it works pretty well, especially as a secondary off-site backup option. But yeah, if there's a threshold of, say, 2TB and > 5GB/day bandwidth that makes someone an unprofitable customer, then they should just set caps accordingly rather than claim unlimited.
As far as I know Backblaze doesn't throttle. I have two computers being backed up (1.5TB and 33TB) and about 2TB being backed up from a NAS to B2. Honestly it's been working without a hassle. Granted, if I ever have to restore that 33TB, it could take a long time, but most of it wouldn't be critical to getting the system up and running again and if it takes a couple of weeks to restore, fine.
I don't think we are competitors.
I have publicly criticized flat-rate storage pricing for many years[1].
That being said, I wish them good luck and will watch with great interest.
[1] https://blog.kozubik.com/john_kozubik/2009/11/flat-rate-stor...