Also a Backblaze unlimited backups user. The Mac app still doesn't autoupdate gracefully on demand using something like the Sparkle framework (clicking "Check for updates" brings up a prompt which takes you to a browser window to download a zip file you have to open and perform a traditional manual reinstall). The mobile app (at least on iOS) is seriously lacking. The restore experience is minimum viable (compared to Arq and Time Machine). Are my files backed up? Sure. Do I feel like I'm getting value? I'd move to iCloud TimeMachine target if Apple rolled it out today as part of iCloud; the value isn't in the object storage (even Apple uses S3 and Google Object Storage on the backend), it's in the backup and restore experience.

Maybe my expectations are too high; I'm looking for a UX as beautifully put together as Dropbox (both on Mac and iOS).

EDIT: I will compliment the ease at which I can pick a filesystem tree and snapshot it to their B2 storage system (say, for snapshotting all of my Apple Photos Library at points in time), but it too has a lot of rough edges.

(using ~332GB of storage for backups, which is ~$20/year using Backblaze B2 vs unlimited backups offering; Arq offers five computers and 1TB of cloud storage for $60/year)