I tried it for a few weeks when it came out. I wanted to like it. I like having many apps/utilities, in addition to Finder, locked to my desktop 1, like Messages, Notes, Mail, Music etc, for tidyness. Most other spaces are full-screen apps.
Didn't suit me. Instead I'm using an app called "Quitter" which sits in the menu bar and lets me quickly set any app to quit or hide after a set period of inactivity. This gives me the tidy desktop, without Sidecar's everpresence and constantly reordering of apps.
It's been a while. Sidecar might have improved, but I found it to have a bit too big of a visual footprint, and too little customizability.