...update...
I've now done 20+ frost free miles, so the Winters should be nicely bedded in.
Three reasons to be cheerful.
1. The tyres roll better than I was expecting - I couldn't detect much difference between them and the previous balloons.
2. They are more comfortable than I was expecting - the Winters are almost as comfortable as the balloons, although I did run those at fairly high pressure.
3. My now over-size mudguards work much better - my ride on Sunday was in heavy rain and the bike didn't get nearly as dirty as it would have done with the balloon tyres.
No significant downsides so far.
The Winters do track and squirm a tiny bit over minor imperfections, particularly the ridged tiles on some cycle paths around here.
Not a problem now that I'm used to it.
Weather forecast is for some frosty mornings next week, so I may get the chance to try the Winters on ice.