I have been told to turn off my Kobo for take off / landings and also to remove my bluetooth headset from around my neck for these times as well. One attendant acknowledged the fact that this was a bunk requirement in my case and was really helpful in explaining why the rule still stands. Basically it's because there will always be that one guy with a 1950's high-power transmitting device and big thick wired headphones that will look at us and say 'well they're not turning off their devices or removing their headsets so I'm not gonna do it either!'. So yes, they know that our modern stuff no longer interferes with instrumentation and present no hazards in terms of dangling wires that become nooses in emergencies. They also know that that one retro guy mentioned previously is usually really loud and obnoxious and it saves hassles all around.
I say rock the Kobo until you're caught
Most attendants have seen me using my Kobo, smiled at me, and carried on.