Should I assume it is not legal in the US to use a TT21 with a TN72 for ADS-B out in an experimental glider? That combination is ok in Europe (I think) with the difference being the US wants 2x the xmit power for ADS-B (TT22 at 250W) vs the 125W output of the TT21. I would like to think that having otherwise compliant, lower power ADS-B out is better (and not illegal) than no ADS-B out in an aircraft that is legal without ADS-B.
Probably not a realistic hope - but it would save me the not trivial expense of upgrading my TT21 to a TT22.

JJ