i have been using Clearblue fertility monitor, since november and found out i was pregnant today!!!
it is really easy to use, has a 6 hour time gap to do the test in each day (so if you don't get up at the same time each day like me it made it easier). it highlighted low days, medium and high fertility days which was brilliant in narrowing down the best days to try. i have only one ovary, and the monitor helped me see whether the ovary i have released an egg, or not! would recommend clear blue. you can buy new ones on ebay and the sticks are cheaper online too!