Hi Home Fairy,
It isn't recommended for people with cycles longer than 45 days but me being me thought aah bugger it i am getting one. I have been using it for 2 months now and the first month i got my peak on CD17 and my cycle lasted 28 days (first time EVER) on my second cycle i did get a peak at all. This could just be because it is getting used to me but because my cycles have obviously gone back to being quite long again it only asks you to test for 20 days. I got my first high on CD13 and it went back to low again on CD27 but in that time i am pretty sure i didnt OV. So now it no longer asks me to POAS and it just sat waiting for me to press the 'm' button for CD1 again which could be a while yet. You can trick the CBFM and reset it to CD5 so it will ask you to start POAS from CD6 but the thing is it means messing around with your CBFM all the time and "tricking it". I am not against CBFM's i think they are fab but it took buying one to learn that maybe they are not for me (even though it is FANTASTIC) and they really are more for people who have regular cycles.
BUT it is totally up to you, you may find you get on with it. I am just fed up of buying countless test sticks and not getting that peak - although that is my bodies fault and not the CBFM

xxx