Since the free app is fully featured, I see the $8 as the paid version, as opposed to just for sync. But I think they're doing themselves a disservice listing it like this. I use Syncthing to sync my obsidian note 'vault', and by having my Mac's Syncthing directory in iCloud, it also syncs notes to my iPhone. This gives you a free◊, cross-platform markdown notes solution. Oh and since Syncthing has a Synology NAS package, I also sync my notes to a NAS.

◊ I just donated to Syncthing for the first time. It's fantastic