Flarm is OK but it is proprietary technology & only works at very short range; 3-5km max doesn't leave a lot of time to react if you're travelling at up to 250 knots in Class G. Also, I can't imagine Qantas, BA or any other airline taking delivery of a brand new A380 and then getting out the sticky back velcro to mount a Flarm unit on the dash, so Flarm is hardly likely to be a universal solution.
The CAA pushed Mode S as the first step on the road to an ADS-B future. The idea was Mode S for everyone first, then Mode S with extended squitter which, if not exactly the same thing, is at least compatible with ADS-B. The CAA's objection to ADS-B derives partly due from their well known antipathy to GPS and also because some of the people running the Mode S consultation had backgrounds as radar controllers and they were not about to endorse a solution which bypasses radar.
AIUI the point of the trials is to show that a low cost (less than $200 component cost?) simple ADS-B can be used as a 'sense and avoid' system to back up see and avoid. If a cheap system such as the Mitre unit can be shown to work, it is much more likely to be adopted by glider pilots (outside Holland) than transponders, and would supersede Flarm.
I do like the idea of being able to configure my GPS moving map to show any traffic passing within, say, 300' vertically and 1 mile horizontally. A traffic service without having to speak to an overworked radar controller.