This is by all means not a free plug-in. After 5 articles you need to pay. Although something is written in the FAQ : " Squirrly SEO Plugin free?
Yes, you just have to install the plugin from the WP directory into your site. Then connect with your email to Squirrly. The Free Version will automatically start. Once you have bigger content marketing needs, you can opt-in to upgrade to the PRO Plan.
Bigger is of course can be interpreted in many ways. But it means more than 5 articles a month. Tst tst Squirly not very nice.