Mike the Strike wrote:

...and what is the downside of operating a new but uncertified
transponder? Can't be worse than getting run over by a bizjet.

Mike

I'd guess the problem is the same as the parachute with an out of date
packing slip. It's illegal to carry the parachute, much less attempt to
use it just because it's the only thing that might save your life.

An uncertificated transponder installation probably has a C/B that the
pilot was told was illegal to set. A conscientious, Japanese visitor
probably thinks following the hometown rules is the right thing to do.

GC