The Boots fertility monitor is just a BBT thermometer isn't it?
I use a BBT thermometer alongside a ClearBlue fertility monitor, as they both tell you different things. The CBFM will tell you when you are most fertile, your temperature will confirm that you did ovulate (well, probably).
I really like the CBFM. I think the sticks work out cheaper than standard OPKs, and it's been detecting my LH surge quite reliably (even the last 2 cycles when I've been taking clomid!).
My temperatures were all over the place, and not showing very much at all, this cycle I switched from temping orally to vaginally, and I've found the temperatures a lot more meaningful and reliable.
There is a standard disclaimer to all of this (where's MeerKats when I need her?!), which is that no method is 100% reliable. When I had my first fertility consultation my consultant discounted all of my BBT charts as non-ovulatory, even though fertility friend had been happily detecting ovulation every month!