How important are meta keywords tags?

They’re not important at all – spammers used to love filling these with anything & everything so these are now generally ignored.

In fact, generally ignored is an understatement. Google has never used them.

That’s why Google became so popular – unlike engines before, Google looked at backlink profiles and words visible on pages to determine authority and relevance, ignoring meta keywords which were spammed just for search engines without being part of the real user experience.