[Plugin: Formstack Online Forms] Complete confusion over the pricing policy

The website says free plugin, the plugin page on WP says free sign. So, why, when you activated, you need to sign up and pay a monthly subscription for it?

I emailed the company (Formstack) and they say they have no knowledge of this plugin. Is it a weird scam???

http://ww.wp.xz.cn/extend/plugins/formstack/