Don't you think a border controler that would want to check you phone would know about profiles and might ask you to unlock the other ones as well?
Sure, they could know about it. It would still be my preferred option to unlock it, and be logged in to that profile than the others. It's not a fail-safe method. Realistically, border officer will look at your ID, travel docs and quick glance at phone perhaps.
Interesting. My proffered method until now has always been simply turn the phone off. Haven't been asked to turn it on yet