To make matters more complicated:
The US plans to adapt UAT ADS-B in the lower airspace and not 1090ES ADS-B.
Spot on. And hatzflyer has an aspect of this right. There is very much a technology standards battle going on.
1090ES is, in many ways, a lousy datalink. It's low bandwidth, and the spectrum is already congested. But it has the advantage that the transponders are already installed in a good proportion of the world's fleet.
UAT was a valiant effort by MITRE at taking a clean sheet of paper and designing a general purpose datalink. As well as being used for traffic info, it could be used for weather and other such stuff. Plenty of bandwidth, and in the US at least, reasonable spectrum availability. But it's another piece of kit that has to find its way into or behind the panel.
When I looked at them, I could see no first-principles reason why a UAT system would come out cheaper or lower power than a 1090ES system. It's all about volumes and certification costs. If any state other than the US were to propose this technology, it would be madness, as it would never get established. But there is just a chance that there's enough volume within the US that UAT will be viable as a technology.