If you worry about having your iPhone attached to the bars, then this is a really neat addition to the Wahoo Apps. Displays configurable info that you select from the App, and controls the music too!
Yes it is VERY expensive, and when you consider you can buy a reasonably complex smartphone for £99 these days, it should be half this price.
The battery on mine (from Amazon) expired after 3 days. Battery is CR2450 3v, a giant aspirin and also not cheap @ GBP4 (from Maplin!), so I hope the next one lasts longer!!