The last time I used our electronic timing system (Brower Speed Trap 2) I set it up such that I started the machine manually by hand and the finish was automatic timing gates.
I triggered the start based upon the first movement my eye captured as I was standing right next to the runners (didn’t need to be at the finish because of the timing gates).
Obviously the gates can be cheated if they happen to be triggered by a hand crossing the beam prior to the body so keep that in mind.
Using the set up I mentioned (on field turf with football spikes) the fastest player I’ve timed so far was 4.55 (this was almost two years ago). This same player averages 4.25-4.31 when timed covering 40yd on the same surface with a stop watch (depending on who’s timing him).