I haven't tried the one you mentioned but I did try another brand (can't remember the name) and had 2 major issues which caused me to stop using:
1.) The water proof screen was so thick it prevented activation of the touch screen even bare handed.
2.) The phone would overheat even in modest 80 degree weather due to a complete lack of airflow.
Minor: It was difficult to install and remove phone. With the set-up below I can remove the phone to go into the gas station or whatever in a matter of seconds. Would even be quicker if I utilized a bluetooth setup but I'm hard wired.
I use an Otterbox for my phone anyways and bought a ram mount holder for the Otterbox. I mounted the Otterbox close behind the screen which protects it from minor weather. I carry a simple 1 quart ziplock bag and pull that down over the phone and zip up as tight as possible (or move phone to tank bag) if the weather is more than a sprinkle.
I use my iPhone 4S both for simple navigation and also to listen to music while riding. If I want to plan a route I break out my 478 and use it.
My wife won't let me whore around with other women, so I whore around with motorcycles - I've never met one I didn't want to take home
2005 BMW R1200GS (Limey - yes it's lime green)
2007 Honda XR230R (x2 - for wifey and I)