The lap timer transmitter looks useful ok, but tripping the lap time yourself with the headlight flasher is not as hard as it sounds.
As accurate as using a stopwatch.
The 'best lap' light comes on when the bike calculates your distance/time is the best run. Its fun to look at.
Can't beat a real laptimer though since if you forget to trip it on one lap, it also messes up the next lap's time too..