I received my TrueRNG one week ago, and it work fine!
I just wanted to launch rngd when I plug the key, and not just at startup. Currently, rngd (both debian and centos versions) are just provided with SysVinit script, and I wanted to use systemd triggers. So I have done this (tested on Debian, with both rngd versions):
Description="/dev/TrueRNG who trigger rngd"
just reload by systemctl daemon-reload and enable if necessary, so now, rngd will start when TrueRNG is plugged, and stop when I remove it.
It could be improve, but it work. Also notice, in /etc/default/rng-tools file, RNGDOPTIONS is multi-options, and systemd pass it as just one option, so rngd don’t start. You should create one variable per rndg’s option for it work, or simply add options on rngd.service
Also notice on my Debian, rngd only start when I use –foreground, but some topics tell to use only –background for centos, so some tests are needed.