You might want to go to
Posted by: mjamja on Oct-28-12 8:44 PM (EST)
the Garmin and/or Magellan websites and see if they have downloadable or viewable manuals for various models. You can learn a lot by reading what is in the manual and even learn what questions you really need to get answered.
Start with manuals for the cheaper units and then compare that to one for a higher end model to see what additional features you can get and how much you have to pay for them.