Would be very interested to know where they get their pilots from then, in particular, who actualy is ensuring that only the best of the best are flying them and that the aircraft are maintained to the very highest standards?
If these are dedicated guys who are military or seconded from a major airline like BA then I see no issue. Their training and fitness would be beyond question.
If however they are being flown on ad hoc charters, who is actualy ensuring the guys up front cut the mustard if the worst happens?
Lets be honest, most GA operations have few if indeed any more than one TRE for a small fleet and standards are , shall we say, variable.
Given the importance of Her Majesty I would feel very uncomfortable if the only assessment of her pilot's fitness to fly her was on a recurrent sim check performed by a TRE who is most probably a subordinate of that guy who will doubtless be the most senior guy on the fleet!
In my book anyone who flies Her Majesty should have proven competence to the highest Military or Civilian standards and be subjected to rigorous and regular independent , non partisan, scrutiny in a simulator.
Don't worry, any old gash pilot will do, as long as he can pass the medical, but if they're going anywhere with a short runway they get HRH Prince Charles to sit in the left seat.