I just tried it, but it doesn't seem to compare that many shops. E.g. if I go to Find-DVD and look up the price of, say, 'Buffy The Vampire Slayer - The Complete DVD Collection' then it shows the cheapest as Amazon, at £91.97. But if use the Pricefriend tool it doesn't even list Amazon! It says the cheapest place is 101CD at £92.69! Ok - not a lot difference on that DVD, but still - it could've been, and the idea is it finds the cheapest!
Also, Find-DVD show the price at 20 shops (plus list another 19 with no price - I assume they didn't find the DVD at those shops) but the PriceFriend plugin only lists 14 shops.
It does look good, but it's not as good as the Find-DVD site, which is a bit weird! Why can't they list all the sites on their PriceFriend tool? And they're missing out sites like Amazon, not minor sites! Maybe it'll improve later, but for now I'll keep going to their site to compare prices.