I don't know how stable your stroke is, but as far as I'm concerned I don't have to count.
If I flip on the left arm, that's 16, if I flip on the right arm that's 15.
The first 25m of all sets, I always flip on left but it's 14 (because it's the first 25, stronger push off, longer glide).
As for the lap counting, I use the wall clock. So I count using the timing. A set off 1:35 for instance is very easy. It goes like :
35,10,45 and so on...
