AH! ARN - yes - I ALWAYS lit and kept the APU running until the GP was plugged in (and working). Handling there was a bit 'flaky' to say the least. On a 25 min T/R, waiting a long 3 mins for GP before shutdown took a big chunk of time away. So much for a 'noise sensitive airfield'
I cannot see much relevance in this discussion of APU policy to those places where the use of APU is restricted?? It really does not matter which is 'cheaper', there, does it?
On the subject of 'cheaper', I repeat my previous:
I guess it depends on too many variables, including maintenance 'deals' for APUs.