When do you use niż vs od?
They are interchangeable in comparisons but with "niż" you should use Nominative and with "od" - Genitive.
Dziękuję. Is "niż" then a conjunction, like in English where "than" is treated as a conjunction, as in "He is taller than I (am)" instead of "He is taller than me"?
Yes, it is a conjunction.