[RealJames]

I think there's a big of an unfair comparison between trained non-native teachers versus untrained native teachers.

Anyone who is trained will be better regardless.

If we are talking about trained native and a trained non-native speakers, it's an entirely different story.

I am perfectly aware of my idiosyncrasies and colloquialisms and improper tense usages etc.

Another important factor is accent.

I, very simply, would never want to learn conversational Japanese from a non native Japanese speaker, hell I wouldn't even want to learn it from someone in Tohoku!

I believe it's entirely sensible for a student to pick and choose the nationality of a teacher based on which accent they want to be more familiar with.

If a student likes the sound of a British accent, then an American teacher is just as improper as a Polish person with native English levels.

It could be argued that someone wants to learn English with a non-English accent, but I've never encountered that, not once.