I have compared it to the cheap phone apps, those are off by a random number of tenths. Also have compared it to the racebox mini. Racebox was fairly close but had a 1' rollout setting that you could check and uncheck that would then change your times.
Dragy vs time slip I have tested hundreds of times, it's 99% within six hundredths, although this year it seems to always be within 3 hundredths.