OTK vs Fertility Monitor

Brigette
I used Clear Blue ovulation test kit last month, and will again this month. I ordered some more test strips for it online, making sure in the questions part on Amazon that they would work for the OTK because they say they're for the fertility monitor. 
So how are fertility monitors and OTKs different? Obviously the monitor is more sophisticated and a lot more expensive. Is it actually used for anything other than <a href="https://play.google.com/store/apps/details?id=com.glow.android">tracking ovulation</a>? If not, why would you bother getting it?