I've got a Fitbit and would recommend them. Mine is absolutely worth the money. Monitoring your steps is just the start, if you get one with heart rate monitoring too you can see yourself getting 'fitter', which is very motivating. It also shows you when you're in the 'cardio' or 'fat burn' zones, so you know you're burning extra calories. It even calculates the calories you've burnt during exercise, which can be heartening, or frighteningly small. It can be a shock to learn how far you need to walk to burn off a KitKat.
The sleep monitor is interesting, but for me, it doesn't add a massive amount.
I like the option to add people as 'friends' and all take a challenge together - it will push you to get a few extra steps in, or sometimes shame you into getting out and about. I have my DDs added and they're very good at cheering me on.
I'd definitely give it a go - if nothing else, once you've bought it, you'll make sure it clocks up plenty of steps every day 