(Which does seem to show off the lack of lag and responsiveness)
Not many people are currently on there, but you can just open another tab and see for yourself. Also has a little live chat which gets a bridge to their discord server, where you can chat with others that are currently on the page.
https://untested.sonnet.io/Sit.%2C+(together)+devlog+002+%E2...
(Which does seem to show off the lack of lag and responsiveness)