AFAIK the tapes are cheap, but tape libs aren't. Considering that they also take up a significant amount of space, I personally don't see them as a viable backup medium for most private users.

You don't necessarily need a lib, though. Especially if you're interested in a use case where you can store data in a go bag, safe deposit box, etc., it seems like having individual tapes would be preferable.

Individual used drives aren't too expensive (or at least didn't used to be). Libraries, in contrast, do tend to be more expensive (and also a lot more trouble to ship).