Castrol Diesel Magnatec is cheaper than that and is a top quality oil, my 300TDi has run on it from the initial 1000-mile service.
Are you really considering buying it from Paddocks via mail-order or are you just using the link to show the oil in question???? A motor factors will stock several brands of oil in all the different specifications and will be a lot cheaper, I can't recomend Halfords as they are about the most expensive place to buy oil.