I tend to fly quadrantals even when VFR, so that if I end up IFR then I am at the right level. Also as most airways are defined as FL then it ensures separation from CAS even with large pressure differences.
However, it is more complicated that it needs to be. Here is a typical real life scenario:
Take off on airfield QNH
Transit a MATZ at airfield QFE
Switch to RPS
Climb above transition alt and set 1013
Transit CAS zone, be asked to switch to their QNH and transit at 6000' QNH
Descend to 3000 on RPS
Contact airfield and be given QFE for landing.
Why oh why can't TA be uniform across the country, say 6k for the UK, and why on earth do I need QFE to land. I was once given QFE and I asked for QNH, and was told by the airfield to set "the fox echo"...