I'm about to enter my tenth year as a TheBrain user, having started with version 5. I just spent a couple of days doing major pruning in TB10. I love it! It is rock solid and intuitive (Mac OS Mojave 10.14.2, Late 2015 iMac). Sure, I can come up with other things I wish it could do, but I'm a happy camper. Using GTD terminology, most of what I do in TheBrain happens above the runway, though for some tasks it is also the perfect tool.
Every use-case is different, but for me it helps to not see TheBrain as a file manager. I use DEVONthink Pro Office for that, and it excels in this purpose. If I need a file to be in TheBrain, I just drag it in from DEVONthink. The file conversions that DEVONthink does are indispensable for getting useful text documents that display well in the TheBrain. I sometimes link back to DEVONthink Groups, or include clickable Table of Contents text documents to point to more complex file collections.
I also don't use TheBrain for daily task management; I use OmniFocus for that. Managing big picture project management in TheBrain makes OmniFocus much more effective.
Lastly, I don't use TheBrain to create mindmaps, though I do often use the mindmap view when working. If I need to design a static mindmap, I use the excellent iThoughts.
I don't know if this post will help anyone, but I just wanted to share that while the road has had its bumps, sticking with TheBrain has paid off in a great deal of mental peace. Thanks to the team.
I'm attaching an image of my top-level thoughts. My TheBrain time generally starts here, or the search field.
iMac (Retina 5K, 27-inch, Late 2015)
3.3 GHz Intel Core i5
32 GB 1867 MHz DDR3