So here's the details Charlie, the Fitbit HR as well as the others can also be used on a computer. It works just like the app for smartphones, but you just have to wait till you get home if friends send you and challenge requests.
I find it convenient to be able to look at my fitness graphs at any time but if your aren't very tech savvy then a computer will get you started! The Fitbits come with a usb dongle (like a flash drive) that will allow it to find your computer.
The program is called the "Fitbit Dashboard" and can be downloaded from the Fitbit website.
Hope that helps!