I created a Synology account to access tech support on my first unit when I bricked it. I recall being able to skip adding an account on the DS918+ when I configured it last year. Here's a snapshot showing that it is not connected to the Synology mothership and what [useless-to-me] features won't work as a result:
One of my important considerations was that Synology is based in Taiwan, not China. The two countries are NOT friends, and I feel safer using something that might be phoning home to Taiwan versus China.
Synology has a full-featured demo of their DSM interface online, if you want to poke around and see all of the features. Just keep in mind that some features (like Active Backup for Business) are only available on the "plus" models, and the "J" models are missing several features that I would use. Hence, my upgrade from the DS216j to the DS918+ last spring.
Oh, and it is probably worth mentioning that I have had zero problems with 4TB Seagate IronWolf NAS-grade hard disks in either Synology unit. I haven't been a fan of Seagate all the way back to the ST-225 artificial reef fiasco in the 1980's, but these are Synology's preferred drives and are winning me back after Western Digital's dishonesty about shingled disks a few years ago.....