I'm a long time user of Tabs Outliner, both extremely happy with it and extremely frustrated by it. By total coincidence just this afternoon I finally decided it was time for me to look at migrating away from Tabs Outliner while setting up a new machine, after having used the extension for something like 5 years, and I started adding One Tab to all my browsers in hopes I can learn to make it work for me.

The good stuff: Tabs Outliner quite literally changed my life. With almost zero effort I can manage the hundreds of tabs I generally have open at any given moment, including closing them, reopening them, and managing them, all with essentially zero effort on my part. It's truly awesome. I used to live in fear of browser crashes and memory saturation and be unable to find the tabs I knew I had open. Those problems are solved.

The bad stuff: Tabs Outliner is maintained just enough to mostly look current in the store and not enough to address the problems It has. I bought the extension, but I can't get it to recognize my Google profile on my main laptop or new machine, so I'm stuck living without the paid features I've bought. No way to contact the developer or anyone, just crickets on the support forum. Export and import is flaky. Crickets from the developer. Will the extension end-of-life unexpectedly because the developer ignores it? Who knows (for someone like me who is dependent on it that's a huge risk). And finally it's chrome-only and I have need to use a variety of browsers on different machines.

I'm excited that maybe you're building a Tabs Outliner like extension that will (hopefully) be at least somewhat maintained. My concern is that it looks like BrainTool expects me to do far more active management of my tab tree than I'm willing to do given the rate at which I'm opening or removing tabs. I generate and prune huge numbers of trees of tabs continuously, but I probably only actively name and organize tree branches a couple times a year. I'm able to look back at the un-named, auto-formatted branches and remember what's going on in the various windows and decide which to open or close just based on the titles of the contained browser pages. If I need to manually and explicitly annotate and label all those tabs and windows, the value for me is gone. The win for me is having something that gets my tabs into a sufficiently usable tree with zero effort from me, so they're always usable and findable by me just visually scrolling up and down a bit. That's the huge value I get from Tabs Outliner. Labeling and naming and sorting and filtering is conceptually cool, but in practice I've never needed anything more than just control-f find some text in the tree of page names (and the reality is I almost never need even that tool, I can just spot the page or window I need visually in seconds simply scrolling around a bit).

So, tl;dr I'm super excited you're building this and I'm the kind of person who has happily paid for a browser extension to manage my tabs and is actively seeking a replacement for that purchase, but I'm also worried you're more focused on a class of annotation that I objectively have no need for (other than very occasionally nesting trees of windows into named folder/tree hierarchies) and which is at risk of taking up enough time as to make the workflow too heavy for me to benefit from. I'm not looking for a favorites manager on steroids, I'm looking for a better browsing history, where stuff drops out of the history tree when I close the tab or window, stays in the tree if I minimize it into the tree, and that lets me drag stuff into a nested tree or name it if I occasionally want to (but I'm not obligated to). That may or may not be what you're interested in building, but it's a thing that quite literally changed my life when I found it and got it working.