Thru the years, FLARM became de facto colision avoidance standard for gliders and many powered pilots recognised that so more and more powered planes and helicopters ar using it - especially after refinements for use in powered machines were made by manufacturer(s). I am using it often when flying in a glider across the Alps and it has saved my day more than once. The bad thing is an overreliance on it, as there are still many non-FLARM equipped gliders around. (not so in France, where their gliding association managed to make FLARM a mandatory equipment and it is practically impossible to fly without FLARM in French glider centres)
I would reccomend PowerFLARM for helicopter use, especially if you are flying in areas with dense glider population - it shows FLARM and transponder equipped aircraft correctly. (there is portable option too)
I would be cautious on apps that are using information taken from open source internet applications, as there is allways a certain time delay and also filtering involved - it could be critical.
The good news is, that UK has the best coverage of ground stations, detecting FLARM signals-effectivelly all mainland UK is covered-but, again, I would not rely on second-hand information.