I had Garmin and TomTom, many years ago, before Google were created.

Few years ago, I started using Google maps.

Google maps has the following problems:
- you can get distraction from the mobile services while driving, e.g. receiving messages or phone calls
- difficult to handle a call while driving, becauae you do not want anything on the screen while driving and the conflict between the voice from each
- no warning when you exceed the speed limit, close to camera, etc. 
- screen size is relatively smaller than navigation devices

If you can live with these problems  (like me), you better save yourself the price of a navigation device. 

In any case, I suggest that you buy a copy of the street directory. There is a chance of something going wrong with the technology. 

The following mobile apps were suggested by some friends. They have the advantage of providing information about seepd limits.

1. Waze
2. Here We Go
3. Speed Advisor (NSW)