Purchasing a GPS System

How easy is the unit to use?
Based on my needs what type of GPS do you recommend?
Explain your needs - a real estate agent may need more features than just a casual user. A delivery service, taxi service, or truck driver may need even more robust features.
Do you have units with features such as text-to-speech directions or a larger view screen?
Can I see a demo?
Are the user instructions for the GPS interactive?
Such as a DVD or on screen tutorial or will you have to read a huge manual.
Do I have to pay a monthly service fee?
How hard is the unit to install?