Serious question to ponder.
Is UA admitting that we don't need to turn off our portable electronics now?
Cause I sure as hell would like to keep mine on (not that I really turn anything like this "off")
FAR 121.306 provides guidance:
(a) Except as provided in paragraph (b) of this section, no person may operate, nor may any operator or pilot in command of an aircraft allow the operation of, any portable electronic device on any U.S.-registered civil aircraft operating under this part.
(b) Paragraph (a) of this section does not apply to--
(1) Portable voice recorders;
(2) Hearing aids;
(3) Heart pacemakers;
(4) Electric shavers; or
(5) Any other portable electronic device that the part 119 certificate holder has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used.
(c) The determination required by paragraph (b)(5) of this section shall be made by that part 119 certificate holder operating the particular device to be used.
Emphasis mine. In other words, an air carrier has the authority to make the determination of what is exempt from being turned off during flight. In this case, UA has made the determination that their EFB is exempt.