Once a year (at least) a student comes to me in tears because the knobs/gears on their machine heads are broken... A family member or pet dropped the instrument, or knocked it off a chair or some other story... Anyway this is a great set of tuners to have lying around so you can quickly solve the problem.
Note: it's possible that installation will require drilling a screw into a new position on the head-stock. This isn't a problem, for most affordable student model guitars.
Of course if you want something more aesthetic, or with a more precise tuning ratio, there are better options out there...