I have used Divi Builder now for 2 years for my client (getwideideas.com) and I have found it very very flexible and pretty easy to use. Elegant Themes do provide fabulous supporting documentation and videos and the 24/7 support is always responsive.
I am however finding I am having to use more and more CSS to handle device responsiveness but that is more to do with devices like the dreaded Apple iPad PRO and my perfectionist nature. But the standard desktop, tablet and mobile options are all built in providing extreme flexibility in web design.
I would say Divi Builder is not only for the experienced website designer, but also for those that have basic or intermediate knowledge too. I do not consider myself a coder, which is why having the ET support team to help me was a critical decision in going with their software.
Keep up the great work ET!