It’s not that difficult;- The audio is no more than a pilot operating a radar advisory service where the ground controller calls the pilot out of blue with a target bearing;- With this they hear a computer generated voice and then look in the clock direction of the light on the matchbox sized display. Surely they can cope with that, bless em.

I amazed with the sensor kit available now you need any equipment upgrade;- military kit is highly optimised to find highly uncooperative targets, monitoring a massive band width, whereas these units are electrically screaming “Hi I’m here, I’ll even give you my GPS coordinates” on a well known frequency.

Unfortunately it is indeed that difficult.

You can't just lob a system into a cockpit or flight deck (even for commercial air transport), it has to be integrated. Potential interference with FBW, displays, warnings etc, all have to be quantified to ensure there are no unwanted impacts on airworthiness. Where do you take your power supply from? Current running through wiring generates an EM field, so you need to know what that does to the rest of your systems. Where do you put the display? Does it interfere with (eg) sight lines during AAR, or generate another blind spot in the pilot's field of view? What training do you need to rank FLARM warnings with any others your aircraft might be producing? Will the display interfere with escape systems (contact with equipment during ejection and the like (OK, not A400))? Is the display compatible with NVGs? What is the logistics tail? Mean time between failures? MEL considerations and operating regs? Servicing? Documentation?

There will be other technical questions too.

How do you get the computer generated voice into the pilot's ear? The one from the box of tricks won't be heard over the background noise in the cockpit of a fast jet or helicopter so you have to integrate it into the comms system, which is a whole thing in itself given TEMPEST testing requirements. Plus you'll probably be needing an external antenna as the amount of metal in most air-frames attenuates the signal too much which as detailed above is a nightmare to design.

Of course I'm amazed the GA world is insisting on using its own propriety standard when there are two internationally recognised ones available, so it looks like we can all play the over-simplifying someone else's problems game.

This reminds me of the discussion about securing cockpit doors before 9/11. The objection was that a locked door could cause structural issues if the cabin were decompressed during a hijacking.
Funny how quickly that got fixed subsequently....

Not really, a locked door definitely works at stopping people getting into the cockpit.* I've yet to see any reliable figures for the percentage of GA fitted with FLARM to be able to estimate a likely reduction in mid air collisions and without that who's to say it's the best use of a limited budget?

*Even if that would be a good thing, see German WIngs 9525

The FAA mandated that all USA carriers should have locked cockpit doors well before 911. The senior cabin crew member had a key.