I wanted to install another outlet box on the opposite side of this wall. This outlet is 15A and grounded via the metal box and BX cable (verified with GFCI outlet tester before disassembly).
Upon opening it up I found the wires too short to comfortably add another line out AND the white wire broke off in my hands due to age.
The entire basement of this 1960s house is armored BX cable. I don't mind replacing it with more BX because it is indeed correctly grounded.
But is there any reason NOT to switch to Romex for this last length of cable to the box pictured?