I've only been back in for 2 hours and I found it really difficult with the mask on.
I've made my own and have been tweaking them to make them as comfortable yet efficient as possible. The kids in both classes took their masks off after about 5 minutes.
They are mandatory for adults and strongly recommend for pupils.
DH has been back in full time and by Tuesday afternoon he had had enough of the mask.
The heat has arrived and it's here to stay (we are near Nîmes, hottest town on average in France), if we get another summer like last year it will be unbearable or anyone working with a mask (unless there is clim, which schools don't have).