It has been quite a long time that people cannot find a mechanical mouse near a computer. But as I used some for quite a long time and I found several flaws in its design, it is a good example to show how an improper design weak the user experience.
The most significant difference of a mechanical mouse between an optical one is the rubber ball inside the mouse. This will cause several problems including poor precision and heavyweight. To make the mouse works normally, the rubber ball cannot be too light and contact with the desk and sensing axis’s very well all the time. After long time usage, users are easy to get tired and may harm to their wrist. Even though, sliding friction between the ball and the desk is inevitable which limits the precision of the mouse.
The rubber texture also has another problem — it is easy to get dirty. Dust, hair and other stains are easy to get inside the mouse as the ball rolling back and forth all the time. The hole in the back of a mouse is quite small makes it really hard to clean. Furth more, the hole holding the rubber ball violate the rule to separate the circuit with outside environment, which increases the possibilities of damage.
The detachable rubber ball also increases the probabilities to loss the ball, especially when kids use one. The round shape makes it hard to find if the ball drop on the ground and roll to somewhere else.
The reason why the mechanical mouse is designed that way is mainly the limitation of the technology that time. It was invented 30 years ago and is replaced by the optical mouse. The latter one is a great solution for all the flaws mentioned above and provides the much better user experience. As a result, we can hardly find a mechanical mouse in the market.