Pair a bluetooth mouse directly with Macbook Air
The mouse has a fixed connection to the dongle, you can not use a normal bluetooth connection
Once the bluetooth dongle fails or you lose it, you can't simply buy a new dongle, since you are unable to pair the mouse to it again. This means once you will end up with a useless mouse

Note: You have to dig a little deeper into the reviews/questions for example here on Amazon to verify that you can not buy dongle replacements