MR16, as per their design specification are not vibration resistant, nor are they supposed to be utilized with a closed rear housing.
That said there are two different types of MR16 LED bulbs - new install ones meant to be used with full line voltage, and retrofit meant to be used in conjuction with the AC transformer commonly found inside the fixture.
The former, will not work really at all, but the second seems fine. My biggest argument against these are that they are not weather sealed, so if your bike sits outside or you rain ride it might cause a nice shocky failure.