I have been using OPKs for about 5 months and got the CBFM this past cycle and used both this month. Like the other ladies, they gave me the same results, but I do really like the FM bc you can use your FMU and the OPKs are better to use in the afternoon, so it was a real hassle to me to try not to drink much and hold my pee for 4 hrs during the day. Plus, you don't have to take them to work with you and sneak around with your sticks all day!! Ha! But, ultimately, they do give you the same results, so if you want to save $, the OPKs work just as well! What the FM does do, is it gives you a "head's up" that your Ov time is approaching, so you have more of a window of when the best time to BD would be! Good luck with whatever you decide to do!