On Wednesday, March 28, 2018 at 10:09:50 AM UTC-4, wrote:

The 2017 (and previous) Spruce catalog says the TT21 is for sport aircraft, meets the standards, etc. Now in the 2018 catalog they added in bold print "DOES NOT MEET USA STANDARDS."

Don't jump to conclusions. You're overlooking a lot of relevant information. Read some of the more recent RAS threads about ADSB TABS Trig etc..

The TT21 implementing TABS looks just like ADSB-Out to ATC and any plane running ADSB-in and so it works just fine for many glider pilots, maybe not everywhere for all glider pilots... it depends.

Don't ask for clarification in this old thread. Go read the more recent threads first.