I think their comparison page does a good job of breaking down the differences (vs Tailwind UI that is) https://railsui.com/compare/tailwind-ui-vs-rails-ui

Do you not use Tailwind? What is being wrapped? Designed and built this all as a Ruby gem, you can one-click install if you want to build prototypes with Rails even faster. I suppose you're not the target customer, but thanks for chiming in.

But this one costs $799 a year.

What does this even mean? Tailwind isn't like Bootstrap; it's a way of structuring styles, not a design language of its own.