POR15 is an excellent product, but there is nothing wrong with Kreem either, if you follow their instructions, and use your brain. I've seen a few "half arsed" Kreem jobs that have turned to #$%*e, but having used both Kreem and POR15 with 100% success, I can see that POR15 could suffer the same problems that Kreem does, if applied incorrectly.
I actually prefer the Kreem kits cleaning and drying preparatory products, their acid based rust remover does a brilliant job, and once rinsed, their MEK dries the tank completely, before the liner is applied. I Kreemed a Suzuki GS1000 tank and with the leftover product did a Honda XR80 tank, that was 13 years ago, and both tanks (to my knowledge) are still in use, with no problems at all.
If POR15 is not applied to a properly prepared tank, it will suffer the same fate as poorly applied Kreem. As an example, the plastic funnel I used to tip the POR15 into the tank (and to drain off the excess once the tank was coated) was liberally coated with dried POR15, but within days, the POR15 started to lift off, because the funnel's surface was not chemically "etched" as the interior of the tank was. I was able to just peel the POR15 coating off the funnel in big strips, it just feels like thick paint.
Folks who complain about Kreem remind me of that saying, "a poor tradesman always blames his tools". Cheers, Terry.