Ah, I had a feeling that I needed to upgrade the firmware, but then I tried and it didn't work. The key was to first hit the "Upgrade & Erase" button and then plug the OPLink Mini into my computer. Now it works, thanks! I was (like with the Revolution flight controller) expecting a pop-up when I start GCS having the OPLink Mini with old firmware connected about incompatibility, and then allowing me to upgrade firmware...