I can see how this can be a huge time saver for me on the front-end - even if just another level of high-fidelity mockups (vs. production).
I find it really hard to justify dropping the money and then my time if I'm working through a web-based cloud service though (vs. a desktop app - even like the ones that call home like Creative Cloud).
We've seen a lot of web-based essential services go out of business. If I've mocked up 100 sites in WebFlow, the company goes out of business, and suddenly I don't have those resource files - it would be an even larger loss to me than any amount of money I had paid to purchase the software.