On going to Europe I think the French law says you have to carry chains & to be honest personally I would not want to rely on socks for that sought of risk.
I’ve been allowed to carry on up from the valley by the Gendarmes using Snow Socks a couple of times from Bourg St Maurice when the roads have been covered all the way down.
(And the two other cars we were driving with both had socks too.)
And have seen loads of others driving on Socks to get to various different resorts all over Europe.
I’ve heard stories about people not being allowed to continue with Snow Socks, but these all seem to be a long time ago, possibly when they were new on the market and weren’t as accepted as they are now.
From my own personal experience, they are now accepted as “chains” in terms of being allowed to continue up the mountain roads by the Euro Rozzers.