You are comparing a very purpose-built chip in the original watch to a general purpose microprocessor in this design. The original won't have a single extra transistor than it needs, and it won't be operating one Hz faster than it needs to. Not a surprise to me.
And in reality, the real-life battery life of the Sensor Watch will drop further if you actually attach actual sensors to it or (I'd expect) start running your own code on it.
And in reality, the real-life battery life of the Sensor Watch will drop further if you actually attach actual sensors to it or (I'd expect) start running your own code on it.