My dad's little four seat hobby plane has both In/Out. You can track him on FlightAware as a result, because it's continually broadcasting its location; it's certainly not rare or sophisticated equipment.
Here's a military Blackhawk toodling around as we speak: https://globe.adsbexchange.com/?icao=ae27fc
https://www.avweb.com/aviation-news/blackhawk-ads-b-was-off-...
> The Army Black Hawk helicopter crew involved in the midair collision with an American Eagle CRJ700 last January at Reagan National Airport had turned off ADS-B because they were practicing a classified flight profile, according to a New York Times investigation.