To support the transition for paid users, this is probably a free release as they work out payment methods, etc. They're moving to an open-core pricing model, which probably matches their previous strategy.

They've always been unclear when it comes to payment and features. Previous to this they had Business and Pro editions in the App Store and Pro was sold as an in-app purchase to a free version while Business was sold outright. Both cost the same and it was hard to compare the two...

If they want to sell the product later, you can bet they'll have clear Buy buttons.