I�used the $ store/tree brand.� At $1 each it worked perfectly for me because my cycles were so whacky and unpredictable.� Would have spent a mint�on any other opk.� I wouldn't have conceived my daughter without them, I swear, because the cycle I got pregnant with her I hadn't Od until cd44 and without the opk we would have given up at that point!� �I also charted on Fertility Friend, but like I said - my cycles were so long and whacky�that I didn't really recognize a pattern and couldn't use my charts to predict anything.� The OPK was the only way I knew O was coming.�Warning: peeing on sticks gets very addicting!� �Good luck� :-)