Well that was a disaster. I decided to try it on my abdomen/stomach (a couple of inches to the side of the belly button).
It clicked on okay (and the needle went in). But then after the 60 minute wait was up I kept getting the message.
"Glucose reading Not available. Try again in 10 minutes" repeatedly over the ensuing 30 minutes (I´m using the official Freestyle Libre 2 Reader).
Then it decided to just give up with a final message something along the lines of
"Sensor is not working please take off and replace"
Then subsequently switching to the default
´No Active sensor´.
´Sensor Ended´ ´Start a New Sensor to check glucose´.
So. One sensor wasted.
Fortunately, I was sent 3 months sensors in advance. So I can replace it immediately if desired (back on NHS prescription in the UK, the three times I had issue happened with the 2nd sensor out of the 2 a month you get - Sod´s Law - so I had to switch back to finger pricking for a short time).
It could be a coincidence, but unlikely. It looks like I´ll have to go back using my arm.