Sidebery is great. I do experience one annoying issue: it's unreliable at saving/restoring the tab tree across restarts. Sometimes they end up as a flat list, sometimes not all tabs show up. Closing and re-opening a few times usually fixes most of the problems, but not consistently. That never happened with TST, but it's bearable.

Development also seems to have stalled while a big new version is being developed behind closed doors.

Didn't know about this! Looks so much cleaner than the other extension

Preferred it while I was still on Firefox (now on Edge)

I’ve been using it for a while, because I kept having performance and stability problems with TST. Sidebery is much faster for me, I recommend!

How did you track down those problems to reside within TST? I've been using it for years with routinely 100's and occasionally thousands of tabs open without any issue whatsoever.

It looks really slick, I'll have to look closer at it before giving an opinion.

I hacked treestyle to look similar, how does it play with vimium?