It did what it said. I did what I was told - thoroughly sanded the walls, removing all loose and flaking paint before painting over it.
The paint (Dulux Easycare) then stuck to the wall - unlike previous paint put on - although some patches did require 3 coats of it rather than 2.
Whether that was because I used Zinsser Peel Stop first or because I used a good quality emulsion ontop of it, specifically recommended to cope with a damp situation, I have no idea.
Better to be safe than sorry! And yes, I would use it again. It was "gloopy" as my grandchildren called it, like glue, so went on fast!