Grammar help please?

Hi there,

Could you please check and explain these sentences for me?

Don't buy that brand as it depreciates rapidly. (Verb)

That brand is very depreciated after a while. (Adjective) is this one correct I wonder??

That brand is very sustainable. (Means very last, correct?)

It is regarded / accounted as correct. (Both words are correct here?)

You are regarded / accounted the best teacher in our school. (Both words are correct here?)

Thanks in advance.