Me thinks the APU is essential. The 400 pounds savings isn't worth the trade off for a majority of operators. Nevermind about small airports with no access to a GPU, what about Teterboro or Van Nuys on a busy day. You'll eventually get one but maybe not when you need it. How about cooling your cabin In KLAS, KVNY, KDAL etc when there is no juice available. I've operated Westwinds for many years ( many with no APU) and the value of the APU was not lost on me. I've spent many an hour waiting my turn for the plug.