The fine-tuners in the tailpieces on a lot of student violins don't last. The choices are:
Tune with a peg only, this can be hard for students or their parents.
Replace the tailpiece. This can be done but it is not an easy job and time consuming.
The last option is this fine-tuner. It is not great for the strings but it can solve a problem quickly, and it works.
It can also be used on a violin which doesn't have any fine-tuners in the tailpiece. In that case I would use the prong type where the ball end fits into the fine tuner.