I was not aware that Hughes Helicopters used it on the interior of their airframes without top coating it. Still does not seen advantageous compared to solvent resistant epoxy primers since you still have to mechanically scuff and clean the surface prior to application, as well as mix and spray with an HVLP gun. Cost and application time appears to be almost identical, so why not use a two part epoxy primer that was designed specifically for use on aircraft?
I'm not interested in joining a primer war / debate (you obviously feel you have made the optimal best choice), but I will try and answer your questions for the benefit of others that might be interested.
I don't know how the cost compares to the product you are using, but ... $130 will buy enough P60-G2 to make almost 2 sprayable gallons (enough for a couple complete RV airframes)
P60-G2 is a self etching wash primer.
It does not require scuffing for good adhesion, just thoroughly cleaned parts.
It drys super fast (when properly applied). By the time clean up of the gun is completed, you can start riveting parts.
Why not use epoxy primer?
Because to use it properly and gain the full benefits....
It usually
does require scuffing and/or etching prior to application
For full Millspec level protection it generally also requires a conversion coating process (alodine) prior to application.
It generally contains a higher level of dangerous chemicals.
It generally costs more (particularly if you consider the extra materials such as alodine).
For anyone interested in reading more about making a primer choice for corrosion protection, have a look at this article written quite a few years ago by one of our local RV builders (Brent Anderson), called Priming - A beginning dilemma (beginning on page 45 of
THIS document )
Many of the products have changed since then, but the thought and reasoning processes used to make a choice are still the same.
The same document also contains the first report of a test of SW P60G2 primer for corrosion protection. It was only about 3 years old at the time (2005) but the test sample is still outside, now over 14 years old, with the same results.