The main difference is the accent (when I was staying in California as an Englishman they couldn't understand me when I said "Kettle" and their pronunciation sounded more like "Keddle")

But accents will always be an issue regardless of which language is chosen.

I think they should continue using English as it's pragmatic but also introduce Esperanto as another working language and encourage its use (I used to speak Esperanto and my Grandfather is fluent so I'm a bit biased I suppose)