Vibration is uncomfortable for you and the client and it can also cause issues with the nail, like lifting as it's vibrating on new acrylic.
Also if it vibrating it mean the efile bit is not turning in one place so moving, so more likely to cut someone if near the skin.
Cheap efiles are not a good investment,mines from ebay often break quickly aswell as noisy and vibrate... I've seen one from a nail wholesaler for under £100 and this one vibrated a lot to.
I have the crystal nails one it's brilliant, kupa is meant to be good and only heard good reviews, the more expensive one from nsi is good too (I don't know about the cheap one from nsi)
hth