Plus "written by cperciva and heavily battle tested by Serious Sysadmins" is a feature I couldn't recreate myself - notice that while there was an outage, part of the reason for it taking a while was a conscious choice to take a much longer path to resolution than bringing up the previous server in the name of paranoia. Paranoia about data corruption is a nice thing to have in a backup system and something I'm happily willing to trade-off uptime for.

However: For backups of bulk data then, yes, it's going to be relatively expensive. I wouldn't put e.g. my media backups on tarsnap, but "use tarsnap for your git repositories and other high value data, and something else for the rest" is both perfectly doable and an approach I suspect cperciva himself would endorse.