The helos would definitely benefit from FLARM as it also warns of cable locations.
What really should be done is have the heavy iron install Flarm or integrate it into the TCAS box.
Mode S or even mode C transponders are a bit rich to mandate installing into gliders, microlights, hang gliders and parachutes (powered and unpowered) to say nothing of the required battery capacity and radiation hazard to an unshielded human body mere inches away
