I would suggest approaching an in-car lap timer from the perspective that it's for fun, subject to a plus or minus x margin of error.
Faster lap times are not necessarily due to improved driver skill. Faster could be because you've done more laps and now you're more familiar with the course; or something on the car is working better / tire temps / brake pads, etc.; maybe it's due to track surface conditions; traffic.
But yeah, I do see the value in it for comparing how you thought a lap felt, with actual data. When I drove at RFR in Jim G's rx7, we were using a stopwatch, and it was interesting to know what my improvement was lap over lap. His rx7 is also race-prepped, and we did not have insurance risk re: timed laps.
What could be entertaining, is if this is a group buy - how will drivers divide time to use it?
