Cats 5 - appreciate the benefit that FLARM brings to the glider community in terms of not false alarming when thermalling. However, the continuing refusal of the glider community to fit transponders does give the rest of us a real problem.
Frankly, modern gliders significantly out perform legacy bits of kit. Having the performance to add a little bit of weight (Trig make transponders marketed as light enough for paragliders for crying out loud!) means, imho, the glider community should step up to the plate and add the same conspicuity measures the rest of the world are using, so we can see them and avoid them, and ATC can reliably monitor them using SSR. Doing so on a voluntary basis will prevent the need for the CAA to mandate their carriage.
Imho though the old argument of weight/power no longer holds water due to a combination of performance of gliders and size/weight of modern transponders (and heaven forbid, two way radios....)