I think the need for one would be motivated by the type of sailing you do. If you plan to race, or are a "tweaker", or always trying to get the best performance from your boat, then go for it. Fractional rigs benefit more from an adjustable backstay (forestay tension, and mainsail shape).
There are a number of different types:
- A split backstay adjust like
this and the accompanying block and tackle system would do the trick (though you might need to make your "split" taller that how it come from the factory).
- You can replace the two lower parts of the "split" with a continuous cascade of blocks and a block and tackle system.
- You could get a hydraulic adjuster on one side.
- There are a variety of manual adjuster (some use winch handles, some have flip out built in handles)