It seems to be enough of a problem that I think the airlines have it
right. No electronic device usage on takeoff and landing and only
permitted in cruise when captain says its ok. (He may not want it on if
in IMC).

I wouldn't use one in my airplane in IMC. Otherwise, since I keep the
airplane upright by visual, I would think it would be ok.

Although I'm not surprised that electronic devices can interfere, I am
a little suprised they can interfere when the cockpit door is closed
and the devices are some distance (several rows), away.

I don't think anyone knows for sure.....