The big thing you get with Teleport that you don't yet get with Tailscale --- apart from entirely owning the source of truth for SSH authentication on your own infra, which is a very minor issue for almost everyone but is a major issue for some people --- is that Teleport gives you transcript-level audit logs of your SSH sessions.

Teleport also has that web-based SSH console (it's one of the better web-based consoles) and the ability to do joint SSH connections. But the audit log is the big one.

Obviously, the flip side of this is that Tailscale's SSH is built in; if you're already using Tailscale, and you're not already using Teleport, you should enable Tailscale's SSH right away; it is hugely better than managing your own SSH service ad-hoc.