Selfhosted

Syncthing is fantastic... once you get it set up.

First, the rough stuff. Syncthing is not user friendly to set up and use. If you want to sync something, you have to go to every device you want to share with and enable the share... for every folder. You can get through this by doing the Dropbox method of just sharing a single folder, but that will have it's own challenges if you want to only share certain files with certain devices or apply different versioning methodologies. All in all, it can get cumbersome.

Secondly, it's a dumb sync tool, meaning that it's not content aware. In your "editing the same note" example, Syncthing will fail. You'll get a conflict notification and be prompted to to pick which version is correct... and even that will be buried in Syncthing's interface that you'll have to go looking for. That specific scenario isn't what it was designed for.

Lastly, Syncthing will occasionally get hung up on syncing a file and clearing the error isn't straight forward.

Alright now for the good stuff. Once you get through all the above stuff, it just works. I throw it on every computer, phone and tablet I own, and I get (mostly) worry-free backups of all my important files synced to my NAS. And it has saved me MANY times.

There are multiple versioning methods, so you can be sure that if you accidentally delete something, it'll be there for you. You can set it to encrypt files on specific destinations, so if you wanted to sync to a VPC, you can ensure your folders are protected from prying eyes. You can exclude files, so those annoying .DS_Store files that macOS throws around don't end up on your other devices.

I use it to backup my Obsidian vault, but I don't use it to sync my vault to other computers. I pay for Obsidian Sync for that.