I have just bought L4D from this site, and I can confirm too, it works! Last weekend the price was even more reduced to 12.41 GBP, so I decided to make the purchase. There was a little issue with the transaction, that is, I payed via Paypal but the transaction didn't work, but I solved it following their info on the website and contacting them via email:
If you would have any troubles to complete your payment via the website you can still pay for the order by a directly via your PayPal or Moneybookers account to our account
sales@dweurope.eu (yes its same account for PayPal and MB). Do not forget to mention the order number in the comment or title of your payment.
Anyway, from now on, you will see me as AngryWolf, and never as Elephant when I play L4D.
