Hi,
Duebendorf is mil only, I think.
We landed at Birrfeld 2002. Bad expirience.
Unfriendly personal, called police after landing due to customs regulations (allthough we were on a VFR flightplan) and wanted 140 SFR (90 Euro!).
40 for the landing and 100 for calling the police!!! After some
discussions it was reduce to 90SFR which we paid.
From my personal expirience, Birrfeld never again.
Problem is customs, you can't choose any airfield for arrival.
Maybe Altenrhein is an alternate.
Joe