Whilst we might not like it the theory behind what gets hard wired into the panel or doesnt is safety. Are the electronics sufficiently robust and resistant to short circuits and fire, do they represent a physical hazard in the cockpit or impinge on the pilot operating the controls or his view, and does the equipment do what is intended. I can see how you might mount the more basic version of the Xaon in the panel (and indeed Zaon even sell a kit) but I have no idea how you would panel mount the XRX given its shape.
The Xaon units were mounted on platforms which removed via a velcro interface. The electronics were wired as circuitry through the panel into a bus, protected by circuit breakers, and used as an approved installation. Because of the mount system, the units were considered removable and didn't require approval; because of the wiring, the installation was considered permanent, and did require approval. While the PCAS unit itself could be removed, the wiring could not, and therefore the entire installation required an approval. To my knowledge, no effort was sought to do this as an STC.
In these aircraft, nearly every aircraft system was modified, and the exterior of the aircraft had numerous other antennas, attachments, hardpoints, fuel tanks, and equipment above and below the aircraft, attached to wings, etc. Approvals existed, and are on file for all modifications in use in those aircraft.
However, assuming for a moment you overcome all these problems, as pilot in command you then must consider what you do when an approved piece of equipment is not functioning. If you get 1 in 100 ghost alarms is it faulty? What about 1 in 50, or as you suggest 5 in 10 or more? At some point you placard the equipment as U/S and the shop either fixes it, the equipment is removed, or permanently maked u/s. You do that not only for yourself but for the poor sod who is next to fly the aircraft and entitled to think that everything not placarded or noted in the tec log is working,
Not in that operation. Upon completion of a mission, squawks were noted, and the airplane became domain of the maintenance crew. End of story.
I reckon both units are designed to "sit" on the glare shield, where the aerial has the best chance of doing its job, wired into an accessory socket if you wish and correctly calibrated to the aircraft as recommened by Zaon.
Which is exactly the case here, save for the "accessory socket." Hard wiring was used for reasons concerning the wiring of the entire aircraft. Additional DC receptacles were available, but in use with other items. The PCAS, heads-up displays, and other field-expedient after-market items were hard wired as part of the installation package.
Sorry but the more I hear the less I am surprised that you encountered as many problems as you did which sort of comes back to my original point that if the issues arent understood dont be surprised if you dont like the results.
Nothing that was done occurred without understanding, without full compliance, and without consultation with the manufacturer. Those performing the installation were not backyard shade-tree mechanics, but avionics personnel with substantial experience.
Again, there is nothing about the operation of the Xaon units in those aircraft that would make them any less "reliable." The fact is that the Xaon unit is a cheap substitute for TCAS. That it costs a lot to the average private pilot doesn't change the fact that it's a drop in the bucket compared to a real TCAS. the Xaon PCAS is a gimmick which has some limited use, but may serve more to misdirect and put heads down in the cockpit than it does to actually locate traffic.
In the darkness it was better than nothing, it was in addition to other means available. My primary concern would be the private pilot that is somehow convinced by those foolish enough to believe the unit is reliable into using the PCAS to locate traffic...or worse yet, believing complacently that if the PCAS doesn't show traffic, it's not there.
Lest this sound far fetched, I see professional crews every day look for traffic with TCAS. I use TCAS heavily, but never in favor of old fashioned, Mark 1 eyeballs. Far too often I hear crews respond to a traffic report not with "traffic in sight," or "traffic not in sight," but instead with "Got 'em on TCAS." This doesn't help ATC, and doesn't really do much for spotting traffic. Most aircraft equipped with TCAS tend to spend much of their operational time at higher altitudes and in positive radar control, largely under IFR with a higher amount of instrument and head-down work.
In the private general aviation arena, conducted at lower altitudes, more frequently in the vicinity of an airport (with attendant higher traffic densities and distractions), by less experienced and lesser-trained pilots, may suffer even greater distractions or detriments from the use of additional gimmicks in the cockpit...especially units which don't provide substantial useful information, or which, like the Xaon unit, provide numerous false indications of traffic that doesn't exist. Aside from the private pilot having his attention drawn into the cockpit where it should be the least, sending the private pilot's attention on a wild goose chase for phantom traffic isn't conducive to a good scan, or to safety in general.