My girlfriend is a runner first, cyclist second. She uses the 405, it works but it's not ideal. The good thing is you can get all the same features of an Edge, like altimeter, you can pair with ANT+ devices like cadence sensor.

The downside - the display is small so you won't get the same amount of data you would with a true cycling computer. The touch bezel system isn't easy to use on the bike. The altimeter isn't as accurate as the Edge models. The biggest problem is the lack of battery life, especially when you get ANT+ devices paired. The device rarely lasts past two hours when using cadence sensor and heart rate monitor. It also isn't compatible with power meters.

If you're looking for a dedicated cycling computer, I'd save up for an Edge and use your mileage points for something else. If you run a lot and cycle a little, the 405 would be a good way to go.