I tried the free and am going to purchase the paid one( purchased as I write this ) ).
I liked the onboarding n the free plugin too. The pro plugin added
I like that other than the beautiful layouts( which are fast to deploy), it also adds a search box or ask button. That shows up like a help box on right ( here a person can search. If they do not find a solution, they can leave a message - how cool is that.
On the dashboard, I also like analytics which gave an insight into what docs are being read( I only tried it with dummy text as of now ofcourse)
I have been looking for a WordPress plugin for docs for months and tried a few, but none had all these features. So happy to buy it, and eager to deploy :)