A little hard to use, but not a bad app – Instant Supercar Review

I've seen it work on a car, but its tricky to get it to work right on public transportation. The speedometer is surprisingly accurate when you plot it down in your cup holder - just start from a static position - and fire it up. If you have a still place to put it, this app should work for you. Headphones will probably make the sound quality a bit better, I don't think the iPhone is meant to blast engine sounds.
Review by JamJam8 on Instant Supercar.