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How to choose a magellan navigation system 
Think of whether you find yourself using gps infrequently. 
Use of an available magellan roadmate navigation smart-or i-phone app, in some cases, is the only system you need in that case. 
You receive all of the same features of the roadmate navigation system through the roadmate app, without the need to carry a separate gps unit.
The problem, however, occurs if your use of the phone frequently interrupts the gps operation. That and other uses may be reason enough to purchase a magellan gps unit.