Re: GPS speedo app for iPhone?
I could be wrong but I don't think the GPS on an iphone is as acurate as a GPS unit. It uses cell towers and wifi to locate you not a satelite. It is acurate enough for traveling and maps but I don't know about calculating speed.
There might be a better ap than the one you have though, in my experience the free aps cant compare to the aps you have to pay for. You know what they say, "you get what you pay for".