If you thinking about replacing your existing or installing a new shower mixer you should read this.
As long as you get one which is “external” ie not buried in the wall, you’ll always be able to get a whole new mixer quite cheaply.
Thermostatic shower mixers blending hot and cold water automatically to achieve the preset temperature set by you. A decent quality thermostatic mixer is pretty expensive and needs to be maintained annually in order to function correctly. A good quality limescale remover is essential for its optional operation.
A manual mixing valve needs no maintenance and a lot cheaper than thermostatic ones. An ideal choice if you renting out the property.