You might be right.
But I see that Syncheck is firing 5 pulses per 2 seconds at different intervals, so there must be a reason for that.
When measuring we always see a tad of variation, which hoovers around perfect sync.
This makes me think that “only having a few claps in a few seconds” won’t be accurate enough.
Also, read the article on the Syncheck page why popular audio/video devices are not up to the task.
That being said. I am convinced that you can get reasonable and usable results using another method.
(Edit)
Just a thought. If you film @25 frames per second. How can you see variations below 1 frame?
Fredo