I don't really believe this. I have never seen a shaver socket marked as intermittent use only. I have used several shaver sockets for charging toothbrushes, MK, Chilton, Wallsall, Homebase Chinese import and have never had them overheat.It is said, shaver outlets are only rated for Intermittent use, whereas Toothbrush ones are rated for continuous use
The only thing to be aware of is the poor regulation. On zero or low load (such as when charging) the output voltage is around 275v, but this applies to both shaver marked and ones marked with toothbrushes. I always advice using the 110v outlet (140v on low load) for toothbrush/shaver charging if they are rated 100 to 250v to reduce stress.

