Well you are the main person here pushing your flyaway story and demanding DJI fix the issue and give you answers yet you bought a second Phantom? and now considering a larger more expensive setup using the exact same DJI Naza controller you claim is not useable due to flyaway issues.
I cant say your consistent as your all over the place and also so worried about flyaway's and at the same time in search of the cheapest possible FPV setup. This easily can effect your ability to maintain control over your quad, with cheap untested radio components that can and very likely will interfere with your radio signal.
Here is a piece from the DJI Naza M manual referring to IOC Home lock mode.
DJI Flowchart indicating GPS switching to ATTI if less then 6 satellites.
If anyone doesnt know how GPS works and the kind of locations where it is likely to struggle to maintain a good signal then they will get themselves in trouble expecting it to work perfectly everywhere when it wont. The Phantom will revert to ATTI mode and also end home lock mode after loosing a good GPS lock. This means flying in these modes in such areas where its likely to lose lock and rely on these modes will cause you issues.
If you think you are in GPS mode and worse still home lock mode and it reverts to ATTI mode the controls will change drastically, you can easily lose orientation and it will fly differently to how you expect AKA "flyway". They may then panic and force failsafe which also wont work properly without a good GPS lock and does not come with a 100% guarantee so dont rely on it but it will still likely save your phantom if needed but not always with many variables.
These modes are great additions and can help you do some things that may be tricky in other modes, people need to be very aware of the limitation's of the GPS receiver and flying location if they rely entirely on these modes. IF anyone is flying in such an area and isnt capable of flying comfortably in ATTI mode they will very easily lose control and orientation which will cause what many see as a flyaway but I would see as pilot error.
I dont drink any DJI coolaid, but if thats what you think everyone must do if they don't agree with you then so be it, no big deal to me just dont try and scare people off flying all together. If people learn what they should avoid I think it will help them much more then people that deny any responsibility to them crashing, losing orientation or radio signal due at least partially to their own errors which could have been avoided and are in no way DJI's responsibility.