Looks like a neat idea. The USB receiver fits into a slot on the back of the mouse for easy storage. Ideal for laptop users I would have thought.
Note: Looks to me like the mouse may be a mini size one. Comparing the receiver to the mouse it seems that way. A USB plug is 15mm long, making the receiver approx 60mm. Comparing the size of receiver to the mouse I'm guessing the mouse is roughly 90mm long.
Regarding delivery options: If all you're buying is the mouse, go for 3 day delivery as it's the same price as 5 day supersaver. If spending over £49.99 delivery is of course free, but that's quite a leap.