I went out and bought a cheap one. Simply tells me my current speed, distance of trip, and total distance. It does help improve speed if you are self motivating. I get my best and strongest rides when on my own riding a cliff face etc. Because of this and my background in weight lifting I need concrete numbers on speed etc. While I dont worry about speed at the time I do time my runs and count the number of walks I do. When riding fire roads and other relatively easy treks I am a speed freak and constantly compare my speed with other times I have hit the trails. It is a preference but one that isn't 'useless' by any means.