What are the reasons to use an LRA vs ERM for vibrations?
In general, LRA's only work at small bandwidth of frequencies (typically, 180-220 Hz). The beauty is, the frequency doesn't depend on the amplitude. You can make it buzz harder without buzzing faster. 

ERM's have frequency and amplitude coupled. The faster you spin, the harder it buzzes.

Depending on your frequency range, either one will work for your application.