Yacht Man,
You say: "The flight deck atmosphere on these Jet2 aircraft must be a sight worth seeing."
In fact, after many years of flying including "reputable operators", I've found Jet2 to have the best on-board atmosphere yet - absolutely zero us-and-them with the cabin crew, pilots working well together to optimise safety and follow SOPs, a no-blame culture and no more than reasonable pressure from management.
Also, there is virtually no in-flight moaning and whingeing - just how many "reputable operators" can claim that?
Let's settle this APU thing once and for all. Yes we do have guidelines to minimise APU usage, but the crew have total discretion to use the APU for heating or cooling whenever they feel it appropriate. If ever you get on a Jet2 aircraft that's too hot or too cold, blame the crew and not Company policy.