Yes it's a CLI REPL, you build and run the binary using the instructions in the README and then create/insert/select from it by typing those commands into the CLI.
Currently there's no way to connect to it like you would a normal SQL db, but you could embed it like you would sqlite.
Lots and lots of home users care more about the few % of performance than the nebulous "extra security".
I have friends who use their desktop for gaming only, literally nothing else, I guarantee they don't care about the extra security a microkernel claims to offer.
"splinternets" already exist though: https://en.wikipedia.org/wiki/OpenNIC, granted, OpenNIC doesn't have one or more nation-states theoretically backing it. That being said the article takes the alarmism a bit far IMO.
Currently there's no way to connect to it like you would a normal SQL db, but you could embed it like you would sqlite.