Question about OPKs

Okay so maybe you ladies can help me. I've read on a lot of posts on Glow NOT to use FMU for opk. Today I bought the clear blue digital OPKS and the instructions say to use FMU for best results. Anyone have a thought/suggestion. Since the digitals are pricey I don't want to waste them but I don't want to miss my surge. I also have a bunch of Internet cheapies to use. Thanks!! 😊