From July 16th, CASA’s Advisory Circular 91-23 “ADS-B for enhancing situational awareness” will approve Electronic Conspicuity (EC) devices and integrated Traffic Awareness Beacon Systems (TABS) for VFR aircraft.
See the full AC here: AC 91-23v1.0
This AC allows VFR aircraft to utilise the ADS-B OUT functionality of lower cost and portable devices, except during the following situations:
(a) in VFR flight at or above FL290; or
(b) concurrently with a Mode S transponder that is also transmitting ADS‐B. An EC device may be operated in Australia concurrently with a Mode A/C, or a Mode S transponder (other than one that is transmitting ADS-B). UAT is NOT used nor permitted in Australia.
During these times the transmitting (ADS-B OUT) functionally must be disabled.
From https://ozrunways.tenderapp.com/kb/frequently-asked-questions/skyecho-ads-b
I use a transponder mode C (no ADSB out) and skyecho at the same time if you are entering controlled air space you need the transponder. The Skyecho allows you to see and be seen by other aircraft for about $1000 buck everyone should carry one. I can see aircraft out to about 20nm intermittently(other sky echo's) and solid signal at about 10nm which is fine. "Real" ADSB I have seen them out at over 100nm.