The UK airlines flatly ban *all* electronic equipment from being switched on during take off or landing. Although the official excuse is always "to protect the delicate navigation equipment", this is demonstrably rubbish as aircraft equipment is pretty well screened and filtered.
It *is* true that in pre CE certification days, certain mobile equipment did have some unfortunate spurii, but CE testing got rid of all of them decades ago.
Which means that we are left with either a) the cabin crew need to demonstrate who's boss or b) the airlines don't want equipment flying about if there is any nasty tail waving or bumps during take off or landing.