I started using it last cycle and I think it's great.
The temperature that BBT monitoring is looking for is your lowest during each 24hrs, and this is at night, when we are sleeping, which is why it's so important to not move when taking your temp.
DuoFertility takes your temp throughout the day and night and averages your lowest temp for the 24hr period.
You also have a team of fertility specialists on hand to ask any questions and talk through your test results with.
Although it's expensive and only takes your temperature, it's far more reliable, less stressful and provides comfort in the way of support if you need it.
Having said all of this, and no I don't work for them, I am only using it now to monitor my temperature out of interest, as we have been advised by our clinic to try ICSI.
DuoFertility have been supportive and have asked to be kept up to date with our progress, since they also agreed with the conclusion of the consultant given our test results.
Hope this helps.
If you tell me how, I can post a screen shot of the application for you.