Trig TT21 in Experimental Aircraft

Hi,

I am looking forward to selling the Trig TT21 transponder in the USA once
they receive approval from the FAA (or whomever they need approvals from).
However, I just talked to someone who told me that his avionics person said
he could install one in his experimental aircraft - now - even though the
unit is not approved for use in the USA. Can that be true? I don't think
it is, but I'm not certain. I would think it would be illegal to use it in
the USA until it receives US approvals.

Best Regards,

Paul Remde
Cumulus Soaring, Inc.