TAG+="systemd" creates many device units; while systemctl list-units may
only show something like
sys-devices-pci0000:00-0000:00:14.0-usb1-1\x2d9-1\x2d9:1.0-0003:1E71:170E.0004-hidraw-hidraw4.device
a simpler altenative like
dev-bus-usb-1-4.device
will still work.
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Credit to @MarshallAsch for figuring this out.