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.