No not really because I kept getting positives and then I didn't actually ovulate. I read that your body can gear up to ovulate, and you get a positive on an OPK, and then not actually do it. I then started temping which was much better as I could tell when I had actually ovulated.
Yes. I used them and found them excellent. I got pregnant quickly and frequently using them. But my cycles were not that irregular - over the years they varied from about 22 to 32 days. I used the clearblue ones and I don't know if they are more accurate than others. They were pretty expensive though, so if you have very irregular cycles it might end up costing you a fortune.