Why do you use Keyword Difficulty estimation tools?

Keyword difficulty estimators like KWFinder, Keysearch and KeywordRevealer are some of the online tools I've used over the last year, year and a half, for my website (no blog, just a simple HTML/CSS website).

I keep seeing the SEO communities generally frown upon this type of tool as they lack the power of ahrefs and the likes. Some argue that one of the main flaws is related to them using MOZ ranking factors in the calculations. Many consider the DA to be useless.

And now it seems like…

Why do you use Keyword Difficulty estimation tools?