In mid-October 2023, a Sling light sport aircraft and a Piper Cherokee operating in the Moorabbin training area, south-east of Melbourne came within 100 metres of each other while both aircraft were flying at the same altitude.
That’s probably happened to me 20+ times over the years when transiting the Moorabbin training area, but I’ve never rang the alarm bell because it probably happens several times a day!
ADSB-IN won’t help all that much in the training area as there are too many turns being made and it’s almost impossible to tell which way the other aircraft is heading without staring at the ipad for 20+ seconds at a time.
I’m not a fan of the 4G ADSB-IN traffic because it’s too latent… you really need a SkyEcho or similar for the direct source of truth. In fact I might made a YouTube video to highlight the difference.