Tehnically the splitter is a bad idea due to the following reasons:
A) The reason Jez has to force it in is becuase its a C7 europlug, not a UK shaver plug, the dimensions are slightly different and could lead to damage to the socket
B) The secondary winding on the isolation trasnformer is probably only sized for the load of one shaver or toothbrush.
C) We are, with shaver outlets relying on a concept known as 'protection by electrical separation' (basically an isolation transformer is used so that the supply is not referenced to earth). Now this is pretty simple to impliment for a single piece of equipment, but there are a number of other considerations for the same source to supply multiple piece of equipment as as such arrangments would not be permitted in a household environment. The 110v/220v shaver points would have multiple secondary windings, so each one only supplies a single piece of equipment