Hey Anton,
I’ve been trying to resolve checking my blood sugar whilst surfing for several months now. Check out the link below to my most recent post. I purchased a 14 day sensor from Abbott (Australian Market). Sure enough the watch could work as a standalone. I went for a run with just the watch and my freestyle libre sensor able to check my sugar whenever I pleased. I haven’t surfed with it yet but judging by the videos embedded in that post it should work. The dexcom system just doesn’t work whilst surfing as detailed in that link.