Skymap disadvantages:
1.Used as a portable, batteries last no more than a few hours. Go and get a quote for proper installation and you'll realise it's then cheaper to buy the colour Garmin portable. (Garmin III batteries last for 7 hrs +).
2. Skymap has no other useful features except the basic map mode. (Garmin III gives you fantastic airfield data, highway in the sky mode, a VOR sort of mode to let you steer an accurate course, flight time, odometer and MUCH more).
3. Skymap needs an aerial attachment with a long wire that has to be suctioned to an area of plexiglass somewhere and this is not guaranteed to stay in place. (Garmins small fold up antenna is fantastic and with over 300 hrs of flying use I have yet to lose signal for more than 30 seconds)
4. Skymap downloads limited (if any?) on internet. (Garmin has fantastic site for upgrades etc.)
5. Skymap isHUGE (and Garmin III is not)
Spils. if you need more convincing send me a PM, there really is no debate!!!!!!!!!!