It is small and it only needed 2 AAA battery's.
The downside of this mouse is that it didn't have an on/off switch.
I regularly travel with this mouse inside my backpack, which happens to move a lot. This causes the mouse to not go into idle mode and it always uses the full battery.
To prevent it I have to take the batterys out whenever I go.
It's somewhat weird that some people do have the switch, but I guess it's just luck if you have one.