The default theme doesn't display very well on smaller screen devices https://www.demo-joomunited.com/dropfiles/default-theme-demo
Especially in portrait mode, the tree navigation is cut off. See attached image.
The issue is that I need to allow my visitors to navigate the nested levels of documents easily. Currently this isn't possible on mobile devices. I don't think a tree structure is good design for mobile screens. Maybe you should consider an accordion, or slide menu.
I'm reluctant to purchase as I feel I may need a lot of customisation, unless you can support that?
The responsive view should be handled of course but it seems something is broken recently.
The responsive view were like attached initially, we'll fix that and make a release ASAP.
Well I hope in a week or so.