I've done a ton of POR15. First off the paint is permanent on your skin, use brake clean to get it off immediately. It likes a rough surface so the rougher the better. So the more rusty the better. You want to scrap any loose paint or rust off with a brush, clean it with the degreaser and then hit it with the metal etch. Then paint with the POR15, then top coat if it's exposed to UV.
The coating itself is very strong and slick as it's sort of like a self leveling type of paint. It does take forever to dry tho and it's really affected by outside temps, so don't do it in the cold. Even tho it's tough, once u break the coating or if it lifts for some reason it will just peel off like a sheet of foil. But if u get a good bond and it's protected it should last a long time. I will also state that paint doesn't exactly need the degreaser and metal etch as it all gets very expensive. I just get the paint and use a lot of brake clean to get it all decreased and clean after scuffing it up. POR15 is meant to be brushed on and I wouldn't put it anywhere u want a finished appearance as sometimes the brush strokes don't go away. Also you can reseal the can, line the top with seran wrap like over a few layers into a square bigger than the can and then lay it over the opening, hit the lid back on with a hammer and it will reseal. Depending on how you do u can also use a large clamp to keep pressure on the lid to keep it sealed. I've done this a bunch of times. Sometimes it will create a thick skin in the can but if u poke through it with a screwdriver u will hit paint again.
POR15 works on the principle of no air and no moisture no rust. It seals the rust from both air and moisture and therefore it can't continue to rust. If u peel the paint off u will see the dry rust like it was before u painted it.