Manual stop watch (MSW) worked for me when I ran my back yard grass track oval. Hung it around my neck on a lanyard.
True, time was lost on the start and stop procedure for the watch, but it was a consistent loss. A loss I accepted as part of having a simple and inexpensive timing system. Reaction time loss to the start/stop was remarkably consistent, so felt I was fairly timing the trucks. The MSW method was also helpful in determining if chassis adjustments helped or hindered lap times.
The two radios I was using to run my six trucks also had Up Timers. Tried those but didn't adapt to them well. That's also an option, but it only recorded to the full second. Using the MSW, trucks could time to the 0.25sec lap. Often a deciding factor in race placing.
Hope this helps. 'AC'