For those subject to US regulations, the use of any personal electronic device (PED) is prohibited by a crew member occupying a control seat from brake release to brake set. An electronic flight bag is only an EFB while accessing required flight material, any other use turns the EFB into a PED.
FAR 121.542:
(d) During all flight time as defined in
14 CFR 1.1, no flight crewmember may use, nor may any pilot in command permit the use of, a personal wireless communications device (as defined in
49 U.S.C. 44732(d)) or laptop computer while at a flight crewmember duty station unless the purpose is directly related to operation of the aircraft, or for emergency, safety-related, or employment-related communications, in accordance with air carrierprocedures approved by the Administrator.