Quite a lot:

• energy efficency: a phone with a screen on will depleate battery very fast. This thing claims 20 h battery lide while actually using it
• readability in full sunlight: most phones are not readable in full sunlight and consume a lot in this situation
• impermeability: while many phones nowadays can withstand some water, this thing is designed to be used under the rain

Is it worth it? I guess it depends on the use you make of you bike…