I've been using the Vertical tabs with Sideberry for a bit. The minified vertical tabs greatly declutters the top of the browser and feels pretty good, but I've got a lot of trees in Sideberry and several panels for organization structure that the built-in vertical tabs can't yet do, so for now most of my navigation is still Sideberry. Tab Groups are something to watch that may help some of what I use multiple panels for in Sideberry. I think native "tree-structure" is a lot more of what I'd particularly want, though.