If you exclusively use vertical tabs (either with CSS or another way), how is it? Did you miss horizontal tabs at all?
I’m trying to switch to Floorp right now from Firefox, where I have both the regular horizontal tabs, and a flat vertical list with the Tree Style Tab extension. I use the later a lot, and while I could keep this setup in Floorp, I like that the vertical tabs can be native instead of using TST. However, it just feels weird to not have horizontal tabs. I think I might miss seeing a bunch of my tab titles at a glance with it, but I have to use it more and see how I feel.
I've tried a lot of different tab management systems. Multiple tree tab extensions, a couple that build off the built in container system, a few different non plugin browser tweaks, and some random other crap for stacking or deactivating idle tabs. None of them fully feel right for me.
I forgot what the current thing I'm using is called and I left the computer at work but it groups tabs into workspaces and has some sort of container integration I haven't fully investigated. It seems lacking performance wise though.
I generally have around 1500 tabs at any time for various topics of research, news or updates for various things. More often than not I find horizontal tabs to be a hindrance and the only thing that could make them worse is if they shrank to triangles and made a sawblade like chrome tabs.