iPhone as laptimer--good enough?

[MikenOH]

Over the weekend at Mid-OH, between the rain drops, a driver in the next garage was using his iPhone with Harry's lap timer app to video the runs. With the app, it provides lap video, timing, a track map and indicated corner forces. you can also add a obd connection to pull in engine speed and other stuff tot he overlay.

From his iPhone the video looked great, but when I looked at a few other videos on the web,using the same app, the video looked a bit jerky or wavy to the point of being distracting.

I'd appreciate views of people that have used their smartphone as a laptimer regarding the quality of the video, accuracy of the timing and the details of their individual setup.
thanks for any help.