I think I can give you a partial answer. I am an insufferable tea snob, so not only do I travel the globe with one of these strainer devices but also a mini immersion boiler, mini tins/packets of quality tea and bizarre strategies for obtaining proper milk (not UHT) when travelling with cabin baggage only.

After 9/11 I was mystified why my bag was constantly being hauled over for manual secondary screening, especially in France, UK, Pakistan and India. In many cases there was frustration between the screen operator and the search officer since the latter couldn't locate whatever it was that was causing my bag to be flagged up. In the end - and it was a French operator who explained it to me - it turned out that the tea strainer looks similar (on the screen) to certain gas operated devices which have been identified as being problematic from a security point of view. Therefore well trained security operators are brainwashed to find them, but the daylight appearance of a tea strainer is of course nothing like the risky item in question.

My solution is to add it to the clear wash bag and always take it out for screening. Can't explain why 2 = ok and 4 = not ok.