It's neither ultrasonic (vibrates ~100Hz) nor ultraviolet (just a purple LED that emits no UV). However, it does clean the stylus, although imperfectly.
I gave up on it and use the Humminguru S-Duo instead, which is a real U/S cleaner combined with a stylus gauge. Either way, such devices are to be used infrequently, as all carry a risk of damaging the cantilever or, in the case of the S-Duo, getting water inside the cartridge. I still use a carbon fibre brush at the start of a listening session and turn to the S-Duo when a loupe shows the stylus needs it.