I had good experiences with POR15(including their Metal Ready product too). My last application was applying to the frame on my 05 duramax and few years ago. I have used POR15 in my corvettes and some customer cars I have worked on. I have never used any of these products on the topside or body, I have cut out the bad areas and repaired.
For surface rust, you need to sand or grind out and use etching primer like PPG DP90 and the the typical paint prep(or have Kevin Clifford to respray) and no more rust from that area.