I avoid any product that claims 'little surface preparation needed'. Having said that I am happy with the results of POR products after I grind and wire brush the surface with an electric grinder and then wash off with a metal prep etchant and a final wipe down with a prep solvent. I'm a proponent of the "belts AND suspenders" school of thought.
I did just that on my floor when I repaired it. No problems peeling a year later.
I had a couple of holes in the floor. Cut out the bad, welded in the good, seam sealed it, wire brushed the ENTIRE floor (scuffing where good, getting deep where scaley), coated the whole thing with POR and then put down a knock off to Dynamat. Everything is nice and solid.
On the bottom I followed pretty much the same process except instead of covering with Dynamat I shot it with undercoating. So far no problems there either.
On the area that is flaking: is it exposed to light? POR will fail under UV light.
