They are if you're taking them at the right time, which is key. Those test strips, otherwise known as "internet cheapies" aren't as reliable for early detection as the name brand tests like ClearBlue and First Response. That's because you don't always know what to expect from cheapies and the labels can be hard to decipher. There are tons of brands of these test strips and some of them might test for a lower amount of pregnancy hormone (HCG) than others, leaving you without a clear idea of which strip is accurate for early detection and which ones need to be used after a missed period.
Think of it this way - internet cheapies are a great way to feed a POAS (Pee On a Stick) obsession since they're pretty affordable. But when it comes to accuracy and consistency, you need to use a trusted name brand to confirm a pregnancy. If you use a name brand to confirm your pregnancy but then go on to use cheapies to track the progression of your pregnancy you may get a false negative because the name brand may be testing for a lower amount of pregnancy hormone than the subsequent cheapie, making it look as though you're not really pregnant or that you're miscarrying when in fact your HCG just hasn't reached the amount needed to turn the cheapie positive.