Which one to choose?

This will depend on the finish required and type of hair to be tidied. The professional range shown here has a replaceable blade system with a nut and screw on the side of the head to allow the blade to be replaced when blunt, or interchanged with another grade of blade if required.

The standard range is a plastic handled tool with fixed blade.  Made with the same high quality steel.  This is a disposable product and tidies 10-20 tails depending on  how much needs to be done.  These blades cannot be re-sharpened