You may consider your hands  in "average" size, but does every mouse feels the same to you? Of course not! Mouse designs are mostly universal but our hands are not. Every different mouse design will result in a different grip. Wrong gripping posture builds up strain and tension in our wrists and eventually cause joint damage or wrist pain, especially for those who work with a mouse everyday. Luckily, people are now paying more attention to healthy lifestyle so there it comes ergonomic mouse. 

Most ergonomic mouse on market is huge and heavy, not ideal for everybody. 

Jelly Comb's vertical mouse 009 is designed for people with relatively smaller hands and it helps enforces a healthier posture to reduce wrist strain. It also comes with both left and right-handed models and a couple of color variety. 

 You may find more information about MV009 here: 

https://www.jellycomb.com/Ergonomic-Wireless-Mouse-MV009-p801612.html