Just have a look at their FAQ to see how badly apple's closed development model hurts applications all over the place. For this application to really work, there's a huge list of precautions you have to take and most of them are based on the fact that third-party apps don't enjoy the same API as the apple based ones do.

The app doesn't work if you lock the phone, the app doesn't support the iPod Touch, the phone needs to be connected to power because there's no concept of different (hardware) sleep states.

And of course, the app would not wake you up if you were to get a phone call or SMS during the night.

Most of these limitations would go away on open hardware with an open SDK.