They say in Taiwan if you properly pronounce "N", others might be confused and would not be able to tell whether you are saying "N" or "M", but if you pronounce "N" as "ㄣ" then everybody knows that you are saying "N".
How ridiculous!
In Mandarin there are pronunciations that correspond, or are very close to, "N" and "M".
N: ㄝㄋ
M: ㄝㄇ