OPK's

Does anyone know how good the cheap OPK's are? I bought some in bulk on eBay and this is my first month using them, according to my tracking apps today is my most fertile day, but I've been using the strips for the past 4 days and barely get any second line at all and it doesn't seem to be getting darker. 
Two days ago my CM was an egg white consistency which I thought meant I should be ovulating soon but so far nothing according to these tests?