I have used a speedometer on my BlackBerry for as long as I can remember - mainly for two reasons. Firstly - it is easier to view my speed with my BlackBerry mounted in my car, rather than looking down at the built in one behind the steering wheel. And secondly, they are more accurate as they fix onto a number of satellites.
Since switching over to BlackBerry 10 I've tested out a few speedo apps and TrueSpeed is the one I always go back to. Mainly because it's a native BlackBerry app and I love its simplicity. Once the app is running all you will see is your current speed surrounded by a colored circle which shows North, East, South and West. You get three color options for the circle which I think is a nice touch.
Also, you have the options to use MPH, KPH and even Knots if you were to take it out on a boat. There's a HUD mode too and you can also override the screen timeout on your device to ensure you can always see your current speed.
The application is available for the BlackBerry Z10, Q10 and Q5 which is great to see and the price of $0.99/£0.75 seems fair to me. The only confusing part is that in BlackBerry World the app is called 'English' but once on your BlackBerry it's named TrueSpeed. I'm not sure what that's all about but if like me you have your BlackBerry mounted on your dashboard or windscreen then you may want to give this one a try?