I've got a Persona that we've been using for contraception, which is what it's really intended for. Soon we'll be TTC #1 and we'll use it for that too. Persona gives you green days when you can safely have unprotected sex without risk of conceiving, and red days when you would risk getting pregnant if you don't use condoms etc. It also tells you when you're ovulating so you can certainly use it to help you work out when to have sex to try to get pregnant. In terms of usability, it's pretty simple provided you carefully read the quite lengthy instruction booklet.
I've just seen this http://www.kgbdeals.co.uk/national/deals/196809/contraception-monitor---mb-bargains---national
do you think it can be used in the opposite way? they are saying it is a contraception monitor but it looks like it functions in a similar way to clear blue which is £70 more expensive... anyone with any experience please let me know, thanks!