Updated: Jan 5, 2021
Below is my personal experience and should be treated as such. It is not a medical recommendation for any particular exercise and any new exercises should be discussed with a medical professional.
Losing strength and mobility in the hands can be devastating, severely reducing the quality of life. With CMT, muscle atrophy in the hands can be expected, and therefore trying to strengthen the hands is an important goal in order to offset any accelerated muscle loss that may occur due to CMT.
Hand strengtheners come in several varieties, with a cheap, easily accessible version being a device that has an adjustable weight load (ranging anywhere from 5kg - 50kg) via an adjustable spring and is usually sold as a pair.
These types of strengtheners are found on different online retail sites for as little as £10/$10 and are very effective for working out specifically the hand and fingers. Using it in multiple grips you can focus on working out either the whole hand, the wrist, or fingers. The lowest weight resistance should provide enough resistance for people with little strength in their hands, with the resistance increasing to a challenging amount for the majority of people. One word of caution is that these devices are unlikely to be calibrated in any way, therefore take the resistance weight measurements with a pinch of salt. I use these types of strengtheners in sets of 4 for 30 repetitions, making sure to focus on the lower fingers, holding the contraction for 3 seconds, and releasing. Even after a regular resistance workout, these strengtheners can bring a focus to the fingers hard to get from dumbbells or other gym equipment.
Powerball is the most prominent manufacturer of what are known as gyroscopic exercise tools, making many different types of essentially the same device; a roughly tennis-ball-sized sphere with a rubber grip around the middle that contains a powerful gyro. The aim of the device is to spin the gyro as fast as is required and to maintain that motion for a given amount of time, helping to strengthen the fingers, hands, forearms, elbows and other areas based on how it's used. Personally, once up to speed I maintain a strong speed for 60 seconds and switch hands, doing this four times at the end of an arm or forearm workout to make sure the wrist and fingers aren't ignored. While it can be challenging to use as first, it is a very versatile tool that has cheap options if you don't want to splash out on auto-starting versions.
Overall, if you are looking to improve hand strength, these tools are just two that I have found beneficial in doing so while being cheap and effective for everyone. If you have found other ways of improving hand strength, or want to share your own experiences, please share them in the forum!