I don''t know what happened, but I posted something, and now I learned it did not come through. However I would stick to the G 48. You don''t need the roar maps of the G III, so why pay for them.
Have you gone to the Garmin.com page where you can compare all their models.
The only point is the display measure. Indeed all handhelds have that tiny display.
Finally, you will need to buy the 12 volt adapter. If you are the kind of DIY, you will only need the 12 volt and data cable instead of the cigarrete lighter cable.
Good luck. Fernando