+1
The TT-22 is a mode S-ES transponder; add a compatible, approved GPS and you're all set for ADSB-out.
GRT sells them along with an adaptor that lets you control the transponder from a GRT EFIS (HX, HXr, etc). They also sell an "approved but not TSO'd" gps for them, of ADSB compliance. They can also be fed with a 430W, 650, etc. Garmin.
Dynon sells a version of this transponder under their own label.
I've had mine for over a year, passed the FAA test and got my $500 (too late for you, now, I think). Works fine.
Edit: If you want to fly up to LVK I'd be happy to show it to you. It's hidden behind the panel, so you'll need to lay on your back to see it!