NAS Time Machine Backup

Only the following options are formally supported by Apple:

- External hard drive connected to a USB, FireWire, or Thunderbolt port on your Mac

- Time Capsule or macOS Server on your network

- External hard drive connected to the USB port of an AirPort Extreme base station on your network

There are NAS brands like Synology and Q-NAP who supports Time Machine functionality but its formally not supported by Apple and using them is on your own risk.

See also: Use Time Machine to back up or restore your Mac - Apple Support

I have a Synology DS416 and it works very good.

It backups 2 MacBooks, I have 4 HDDs so if one of them die I don't loose any data. Also I have the TM backup data synchronized with BackBlaze, so I have another copy of all my data outside my house for a very low price (I have 1,5 TB for TM synchronized).

I also had in the past a Drobo unit, is good for one MacBook because it need to be connected like an external HDD but if you have more than one and would like to get TM working every time you connect your MacBook your home network, a NAS is a great choice.

I hope this help you.

On the NAS how would you prevent other users from mounting your backup on their own computer? Not that it makes any sense. I don't think the restore would even work. Its more of a security concern than anything.