Efiles (electric files, drills) are very safe when properly used. As with any type of machine, drills are safe when properly used by trained technicians. It is not the machine that is dangerous, it is the improper use by the operator that creates a potential for damage. There are safe electric file training classes available in each state for licensed professionals, and some states are now requiring a certificate of completion of an electric file course before a technician is permitted to use on in a salon.
Electric file bits should be cleaned and disinfected after use on a single client. If the bit is visibly dirty, make the operator stop and replace it with a clean one. If they refuse, leave the salon. If the operator is using sanding sleeves, these are single-use disposable items and must be discarded after use on any one client. Do not let an operator use a visibly dirty sanding sleeve on you.