Looking at the various options on Amazon, it seems that Fitbit devices cost between double and 4 times as much as alternative brands. I suppose its the usual suck-the-suckers-in approach. I recently earned my "Russian Railway" badge, indicating that I had walked well over 5000 miles in the last 6 years. Such things don't normally matter a damn to me - until I realised that my old college pal Audrey, whom I haven't seen since 1975 other than on facebook - was posting about her fitbit achievements.
I suppose anything will do that records my paces, and ideally talks to my iPhone .There are some pretty cheap ones whcih also record GPS tracks. But then the iPhone can do that anyway.