As usual, I forgot the steps to get this working on a fresh install, so documenting here.

Fresh linux install. Get Tvheadend installed. It detects the USB device but nothing works – won’t tune/scan.

Remembered to check dmesg output: it says couldn’t find firmware.

To resolve:
Download this firmware file below to /lib/firmware, and reboot. (remove the .txt extension, wordpress wouldn’t let me upload it…) This file was originally found at http://palosaari.fi/linux/v4l-dvb/firmware/Si2168/dvb-demod-si2168-02.fw

Notes:

* Do not download the version of this firmware found on the openelec site (https://github.com/OpenELEC/dvb-firmware/blob/master/firmware/dvb-demod-si2168-02.fw) this doesn’t work, I don’t know why, you get an error like this:

* Also, do not download or put in the firmware directory the file called dvb-demod-si2168-b40-01.fw which you may see a message about in dmesg. Again, if you try this one you will get an error.

Use the small file I said, and after rebooting and loading tvheadend, finally get a successful message in dmesg:

List of all licencees: https://www.blu-raydisc.info/licensee-list/discmanuid-licenseelist.php (basically anything that is not single layer is always HTL type)

French study looking into archive quality of different brands: https://club.myce.com/t/french-study-on-bd-r-for-archival/302333

Panasonic followed by Sony are the best for longevity according to the study. However, neither are widely available outside Japan.

Acu-disc are a supplier of HTL discs widely avaiiable in the UK and have good reviews, although no independent evidence to compare them to the big name brands https://www.rpadistribution.co.uk/5060158312948/Acu-Disc-%C2%AE-Blu-Ray-10x-White-Thermal.html

The diagram on that page looks exactly like a Panasonic one – maybe they are the same fabricator? Possible, but after contacting BlyRay licence office, they said “As they do not use the BD Logo ad have no license from us, we cannot guarantee that their products are legitimate or compliant.”