In the US each new ATC sector gives you their altimeter setting below 18,000ft. It has the advantage about not having to worry about what you real altitude is versus flight level but it also means you have to change altimeter settings a lot.
On balance I don't like the way at the moment different parts of the UK seem to work on different transition altitudes, I can't see any good reason for it and it would seem sensible to just have one. The US uses 18,000ft so that seems as good as any other altitude to use...