I thought about getting one of these, but in all honesty, the OPK has worked so well for me, I decided to skip it. I do buy the more expensive brand of OPK (ClearBlue Digital) and it still costs about $50 per month, but it takes away the guess work for me, so it's worth it to me. I know others here use the monitor and love it. I just haven't been able to justify it.
Good luck whatever you decide!!!