I used the Persona monitor, which is designed for contraception, not TTC (although it worked well for me as both). I'd used it for several years as a contraceptive, having failed to get on with the Pill and then having a disastrous coil fitting.
I've not tried the CBFM so I can't compare but I really loved my persona - it helped me become very aware of my cycle ie I would start to notice the difference between CM before and after ovulation. I had a very regular cycle which also helped.
I used to buy the sticks on Amazon or on ebay as they're much cheaper, and I would also buy them in 6 month batches (after contacting the suppliers to make sure the use by dates were long enough) which helped keep the cost down.
As for using it for TTC, we used it for contraceptive initially, sticking to the rules-ish about 'red' days, and using the withdrawal method (sorry, TMI!). After making the decision to TTC, we went for it on red days and particularly when we had the OV symbol - got a BFP two weeks later 
The only drawback I found was having to make sure I tested with FMU during the testing window - cue peeing in jam jars if I woke up at the wrong time!
But I'd recommend it to anyone - although I have a standard 28 day cycle, I ovulate around day 11-12. By the time I reached day 13-14 which is when the NHS say to TDD, I was already back onto green lights (ie no longer fertile). Heaven knows how long it would have taken us if I hadn't had the extra knowlege the Persona gave me....
Sorry for the lengthy post!