Upstream has been providing a very thoroughly designed set of systemd units,
udev and polkit rules. With these the brltty daemon is activated
asynchronously via udev, runs as a dedicated user with runtime and state
directories set up using systemd-tmpfiles.
This is much better than the current unit, which runs a single instance
as root and pulls in systemd-udev-settle to wait for the hardware.
Otherwise it starts way too early, only to fail and having to restart
until devices are available. It is less wasteful to simply wait until
there's a reasonable chance of success. This is consistent with
upstream.