I've only been using the system for a day or so and have been focusing on white-labeling and how I can use this to collaborate with clients rather than the Page Builder. So far, I am very impressed. Although not immediately obvious, and there is little documentation on the subject, their support is fast and very helpful, especially for 10pm on a Saturday night!
The Page Builder looks powerful and relatively easy to use. I still need time to learn the system but, I don't think it will take long and if I do run into problems, by experience, I know that help is only minutes away.
For those that purchased Bookmark.com, it is quite similar in some ways but this one gives a lot more control over the modules and elements, which may be a good thing, or a bad thing, depending on how much control you want to give to your clients.
For the price, I thinks it's a real bargain and well worth purchasing.