Yes you understand the suggested approach. I don't know about the mariadb tool and if it looks good, by all means use it, but I would offer that the fastest, simplest way to restore a reasonably small database that I can think of is with a sql dump. Any additional complexity just seems like it's adding potential failure points. You don't want to be messing around with borg or any other tools to replay transactions when all you want to do is get your database rebuilt. Also, if you have an encrypted local copy of the dump, then restoring from borg is the last resort, because most of the time you'll just need the latest backup. I would bring the data local and back it up there if feasible. Then you only need a remote connection to grab the encrypted file and you'll always have a recent local copy if your server goes kaput. Borg will back it up incrementally.

Also what is the reason not to use the mariadb tool provided by borg?

I don’t know what tool you mean and can’t find any references online. I do see that Borgmatic allows hooks to run a program like mysqldump before a backup run, but it’s neither part of Borg itself nor has anything to do with streaming data, so I’m still confused about what tool you’ve found.

The advice you’ve gotten is good and it’s what I do. A cron job runs mysqldump, a different cron job runs borg, and I do error checking on both of those as well as occasional test restores.