Ergonomic, practical and attractive
The fairly flat, relatively wide shape makes for a fairly firm grip, which I think is a good idea. The rubberised sides make it harder and easier to grip. The two batteries add a considerable amount of weight.
One of the great things about this mouse is that it can be used with three different devices. Using it with a smartphone or tablet is a pleasant experience (precision, fewer fingerprints). The fifth star could be given to it... but in a few months' time for reliability and/or solidity.