I've flown in gaggles. I don't see how any electronic displays and/or sounds can replace "see and avoid" attitude in a gaggle, with distances of just tens of meters. You have to turn your neck/head/eyes around all the time rather than be distracted by the instruments. I believe devices like FLARM are useful at distances slightly bigger than those in a gaggle. Please correct me if I'm wrong. I have no experience flying with FLARM.

Tom BravoMike