One problem with using RPS in the UK is when flying below a CTA where the base is notified as an altitude; the RPS can be low enough to cause the pilot to infringe if they try to fly just below the CTA.
I once watched a stream of Hercules not talking to Farnborough or Gatwick crossing MID VOR south eastbound all indicating 2,700ft where the base is 2,500ft (this was in the days before the RAF recognised the 'rule' about using an actual QNH when flying below a TMA) because they were using the Chatham RPS. Particularly annoying for Gatwick as they were landlng on easterlies at the time.