I have the sky demon device, and even though I have a full IFR panel, Garmin 430W, and a yoke-mounted Garmin 795, I still can't bring myself to leave the SkyDemon at home. The three things it does really well are NOTAMs, Airspace warnings and the fabulous side view nav which shows you airspace above and below you rather than just around you.
As JW411 alludes, though, you don't need to buy the actual device. You can try running it on pretty much any windows enabled GPS device - such as a GPS enabled laptop. But for me, I just liked the peace of mind that the device was specced specifically for the software, so I didn't need to think about it.
Last edited by SDB73; 25th Nov 2011 at 19:05.