I'm already in the Piper Owners' Association, and I posted this same
question to that forum at the same time as this group. The one reply
from someone with experience with Avion said that they suck, and the
owner is a liar, and that a FSDO simply will not issue a field approval
for yokes, but that they need an STC. Now, my FSDO says a field
approval is possible, but it's going to be a pain as the relevant parts
of the FARs demand inter alia testing as to the forces the yoke can
stand. He'd much rather find an existing 337, but no-one at the Owners'
Association has come forward with one, and Avion aren't replying to my
emails...