I had the chance to view the Skydemon mobile thing a few weeks ago and I've got to say I was very impressed by it.
The think I like about SD is that the desktop application and the handheld intercommunicate so you can send your flight plans to the handheld device. Not only that but it downloads the notams & weather onto the handheld device so you get a visual representation of them in the cockpit (at the time of download of course).
I use a Garmin 496, Aera 550 and Garmin 430 as I prefer "proper" aviation GPS's. The 496/550 are brilliant VFR aviation GPSs with a host of functions, but I could see the SD as a useful backup if you could mount it suitably. The 430 is only really good for IFR, which is why we run the 430 and Aera at the same time.