"Just be thankful you don't have fertility problem."
Exactly.
In the 16 months of trying for DS1 I found, via OPKs, that we had to have sex the day after I got a positive on one of them. Not the day of, or the day before, or two days later, but the day after. And then 1 had a miscarriage, and then another - the same pattern each time - I was only successful if we shagged the day after getting the positive.
After 16 months and 2 m/cs (which is nothing compared to some people), isn't it understandable to want to start pinpointing things somewhat?
I also had very little, if anything in the way of external ewcm, so couldn't go by this indicator.
Lastly, I found OPKs much less of a hassle than temping and charting, which just felt too much like a military operation for me.
OPKs I could fit into my day quite easily, without it taking over my life - the way I envisaged charting to do. Plus, charting only tells you that you ovulated in hindsight - not when you're about to ovulate which is where OPKs come in.