You shouldn't need one...the stock cooler would perform fine, unless you wanted it to run cooler and perhaps quieter depending on the actual cooler.
What is the link for the cooler?
If you leave the stock cooler on, you'd likely have a much better chance to get a replacement from the vendor if it dies. I'd suggest making sure your case has good airflow before concerning yourself with a replacement air VGA cooler.
Heatsinks and fans for video cards have been around for ages. They are not as popular as they were 20 years ago.
I just happen to be shopping for a new Radeon HD 6850 video card. I read quite a few technical reviews. The stock gpu heatsinks and fans that come with the video card are adequate. If you want gpu temps to drop a little more, then you best bet is the Asus EAH6850: