I've used it for years and it works great. The key, like in most things, is the prep. I used it on my Jeep frame about 10 years ago and it's holding up great. It is sensitive to UV exposure, so it should be top coated if exposed to sunlight.
They had a kit years ago that I bought that came with a cleaner and a rust converter stuff to use before the POR15.
I think it's great stuff and have had good experience with it.
I have used it on the bottom seam of a truck tailgate as well as a place on the inside bottom of the drivers door. It's been about a year. I have already noticed some rust poking back through. I have a lot of friends that have used it and not reported any issues so I am going to guess I fowled up the application. I was very careful and followed the directions to a T. Applied 2 coats. Even at that, again, with no bad feedback other than my own experience I am willing to write it off to something I did.
Everyone I've talked to who's had an application "fail" due to "improper prep or application" blames themselves. Few people say "I use it, it's flawless, works great, lasts forever".
I just don't think it's that great of a product. More hype than it's worth. Good prep, good paint, clear it a few times, it'll last.
it does what it says. if you do your prep properly. i've used it on my baja bugs for years. i always have the pans blasted before i start and i've never had a problem.