I had the Sigma BC1609, but it wasn't great: lights interfered with wireless signal and cadence sensor stopped working. Give yourself a treat and get a Garmin Edge 500. Motorola ANT+ speed/cadence sensor is £19.99 from Evans right now. Add a HR strap or even a power meter later. Upload to Strava or Garmin Connect, program workouts for training, upload courses from RideWithGPS or Bikeroutetoaster, race against a virtual partner, ... Easily the best cycling accessory I've ever bought and so much more than these other computers.