It is our considered opinion that most fitness bands don't do a lot to get you fit.
Walking 10,000 steps per day is absolutely better than doing nowt, but it won't turn you into Mo Farah.
It's also questionable how motivating many bands are, and how useful the data they track is. We would particularly question their accuracy when it comes to calorie burning, which makes them all but useless for those seeking to lose weight by consuming fewer calories than they burn off.
That said, we know a lot of people find the data on how many steps they've taken, and how well they've slept, to be interesting in itself, even if it doesn't spark lifestyle changes.
If you just want to track steps and sleep, you have two options: go cheap, with a budget fitness band, or go stylish, with a hybrid watch, containing a motion sensor. We recommend the Jawbone UP2 in the former category, and the Withings Activité range from the watches-with-fitness-tracking camp.
There is no functional difference between a step counter costing a tenner and one costing £500. However, many guys are going to be more likely to wear something that looks like a cool watch every day than something that looks like absolute arse. Which most cheap fitness trackers do.
At the higher end of the market are fitness trackers that are more like running watches in terms of functionality. These can track your heart-rate during workouts, which actually is helpful.
The best of these bands give you a score for your overall fitness, as well as targets and tips on how to improve it.