The way we were able to customize our look and feel for our application. The most useful feature is that it's easy to use for both beginners as well as experts. We haven't experienced any major issues using this tool. It has been a great experience working with DHTMLX. Very good customer service through their forums and ticketing system. I would highly recommend this product if you are looking for something simple yet powerful! We wanted to create an app similar to Facebook but without all the unnecessary features. This helped us keep everything very minimal. The best thing about this is that it has such an easy to use interface which makes creating things very quick! I haven't found anything at all so far but one small issue i have noticed was when you upload your own images or pictures they don’t always display properly as there isn;'s enough room in my page (when viewing mobile version). It's great because its free unlike other tools like bootstrap where if something goes wrong then u need pay up front before getting help/support etc..