Have you used Mugen Power?

Have you used Mugen Power extended batteries? I’m planning on buying one for my SGS2 and Nexus S as you might know, these android phones are bad with battery when it comes to 3G and GPS.

Here’s the link to the product. A test or a review would be highly appreciated.
http://www.mugen-power-batteries.com/samsung/samsung-galaxy-s-ii-i9100/mugen-power-3200mah-extended-battery-for-samsung-galaxy-s-ii-si9100-with-battery-door.html