Clearblue Fertility Monitor!

Jessica • 31, married, mummy to DD born on January 1st 2011 and DS born December 28th 2016!
Does anyone here use the clearblue fertility monitor? We're thinking of investing in one as they look so easy to use and are apparently super accurate. Do you think it's worth the investment or are the cheapy ovulation tests just as good? Thank you in advance! X