Kenko Black Mist Protector

I'm considering to buy a second handed Kenko black mist filter protector for roughly 20 usd.

I'm a beginner and never used these kind of filters, so do you think this filter is a good start, or should i buy a different brand? I use Fujifilm XT-30.

Also, how does this filter work? How will it effect my photos, and, is there any tips for adjustments when using this filter?

Thanks!