ADSB has been implemented in Australia on 1090 MHz and it has been mandated for all IFR aircraft. UAT, the USA, system will not work in Australia so don't buy it. Some vfr aircraft in Australia have installed adsb but the equipment is very expensive. ADSB for vfr aircraft in Australia will be non mandatory so it has to be priced well so the benefits can be justified.
Relaxed standards for the devices, their installation and maintenance is required to achieve this. The greatest benefit for vfr flight is an aid to see and avoid. You need both adsb in and out for this and then you see others and be seen. The manufacturers are gearing up for this now with new products. See uavionix web site for example. Small adsb out devices can be put on drones so they can be seen by Adsb in and TCAS. CASA and industry are working on vfr adsb in Australia now. UK have already come out with their system which is a conspicuity system, be seen and they will avoid you. USA has gone UAT with data uplink for weather etc but is very expensive for the ground system. All of the rest of the world so far has gone 1090mhz for adsb with one ground system. ADSB uses an S mode transponder and to get access to some airspace you need a transponder. You won't need a separate transponder if you have ADSB.