POR15, undercoat, or sprayon bedliner?

I have heard from a really meticulous painter / hotrod fabricator friend, that por 15 tends to bond poorly to sand blasted metal and he does not use it but rather uses Spies Hecker epoxy / bare metal primer. I have seen Spies Hecker epoxy primer painted on the inside of engine blocks and remain bonded for years. His co-worker has used por-15 several times and the feedback is that it appears to bond long term - better to very coarsely ground or scratched metal rather than smooth sand blasted metal.

I cant understand why it would not bond great, as long as quality prep work and metal etch is performed to the base material prior to application.

It appears that both the eastwood product and por15 are catalytic hardening by the moisture in the air. That and the other information and reviews I have seen about both, make me think they are practically the same product.

I dont know what to use on my sandblasted metal. Probably an epoxy type etching bare metal primer like fellers have:

http://www.southernpolyurethanes.com/Product Info/Epoxy Primer.htm

I just want the hardest most bonded base I can get.