Ovulation strips-helpful or waste if time?

How many people do you know, or have yourself succsessfully gotten pregnant when using the ovulation strips? I have mixed feelings about using them, some ppl say they are great & got caught quite quick using them & other ppl are telling me they are a waste if time... If anyone can give me advice or share their own. Experiences that would be a great help... Also if you do have 2 strong positive lines on the strips (when your suppose to be ovulating) do u have sex before , during or after the lines come up? Thanks x