This is kind of like Bootstrap Studio [1], which I use all the time. The only difference is that Bootstrap Studio is a bootstrap project IDE. It has components, but you can also edit the content, add your own HTML, export, hosted preview, local preview, its not a service, and ALSO has a lifetime price of only $60.
That said, I think the quality of your shuffle components are better than most of the components on Bootstrap Studio, so I bought it.
All I'd really like to see is the ability to edit content. If I'm doing a prototype for a client, I can't have everything saying Pied Piper or New Internet.