Tarsnap's model is an ideal fit for a very small subset of the data I'm interested in safeguarding for the future. https://andrew-quinn.me/digital-resiliency-2025/ goes into it in a lot more detail.
If you're interested in safeguarding data for the future, then I don't think the model of “my backup immediately disappears once the account runs out of money” gives me anything resembling a cozy feeling at all.
That's actually one of my favorite features. That should never happen under the limited circumstances I use it for. If something goes so wrong that my account actually runs out of money before I notice, then I far prefer the default to be "intruder alert, intruder alert, wipe everything". There's a reason it's marketed as backups for the truly paranoid.