Yea, after some research: the 5th protects your brain - that is pins/passwords etc. you'd rendered and these would lead to self incrimination. These necessarily you'd have to 'retrieved' from your brain. Apparently, they can unlock the phone legally with your face and perhaps with fingertip. So the advice was to power off the phone so the pin is necessary. However, not unlocking the phone would make them to impound it for some time, weeks likely. They still have to make a 'reasonable cause' to do so, and for the phone to be force opened they'd have to have a judge warrant. But since 'reasonable cause' is not longer reasonable in this country, they will make your life unconvinient by holding the phone.