I have the Fitbit Zip (so only a pedometer) and it is linked to My Fitness Pal account. I log my food in the MFP account and can either sync them on my iPhone or it does it automatically when I am near my computer.

Since I started using them, I have lost almost 14kgs. I started in August last year so going slow but steady. Only another 16kgs to go until I re-evaluate to see if I am happy with where I am.

I highly recommend them. I did have an issue with the case where part of it broke off (a plastic part over top of metal) but used their customer service centre via the website and a replacement was sent out without a problem and very promptly.