There an interesting new technical report just out where 4 independent test labs (the IRT, Orange, the RAI and the EBU) teamed up to perform subjective tests comparing HLG and PQ10 as well as native SDR vs SDR from an HLG bit-stream. Results show PQ10 and HLG providing a similar user experience and also that HLG backwards compatibility works from a user experience point of view.
You can download the report here from EBU’s web site.