Works well on the HTC Wildfire. I like it because it works, just using voice instructions with the screen off or with other apps in the foreground. It has a host of options to adjust for individual requirements.
It’s saved me from several lapses in concentration. I’ve checked my speed, and sure enough, there was a Camera Van around the corner. If you are an HGV or PCV driver, you’ll find this app very useful. I know I do.