Other Account's Exclusive Hashtag | Should I Use It?

There is an account with almost 16k followers in my niche. There is a hashtag which is exclusive to their posts only. So Should I use the same hashtag in my post ? It has got a 600+ posts.

Depending on your purpose, if you just want to compete with them why not haha. It'll definitely piss them off but its not against TOS

The goal generally of a person having a "private hashtag" is so that others will use it furthur building the brands presence with that said if they have a faithful 16k following using there hashtag will resonate with some of their fans but not with others.

So long answer short - Yes of course use it capitalize