The Norgie boxes certainly perform well. Really happy with mine - still ice in them on day 5 on the one I didn't keep opening and closing. As with any cool box, it#s best to put stuff in cold as possible, and fill any empty space as you're removing stuff with newspaper or something.
Each box holds a full 20 litres. Mine were £20 each from "ecerslike" on ebay. So 40 litres of good storage for £40. The Igloo Legend 38 litre box is £60, or Igloo Maxcold 47 litre box is £85, so cost per litre the Norgies boxes are good value. Very very tough as well - virtually bombproof. And they clean up well inside with a bit of bleach followed by baking powder.