This is my first year to use them. I tested three mares. Two showed positive and one negative. The one that was negative had been pastured with my stallion, but had shown heat about four weeks earlier. (I was wondering if she might be one that shows heat even after bred, but apparently not.)
I later tested three mares including retesting the one that had tested negative earlier. She tested negative again. This time I was really disappointed. I wondered if it was right, but then a week later she came into heat again. I guess maybe she needs a checkup by her gynocologist.
On the other two, one tested positive and one negative. The one that tested negative has her first foal this year. Last year I had two mares that had their first foal and neither of them bred back until after their foals were weaned, so I'm not too worried about this one.
I bought mine before the price went up, but now it is almost as cheap to have an ultrasound as it is to buy the test. The biggest problem is taking them to the vet.
I am not breeding any this time of year because I don't want any new foals in this opressive heat. I will try to catch a few mares for September or early October babies next year.