I use the 3-2-1 strategy for backups. I keep one copy off-site by using cloud backups, currently I primarily use Backblaze for that purpose but am considering alternatives for several reasons. I keep a second copy on an external SSD via Time Machine, and I keep one copy on-device. I'd like to use network Time Machine to get rid of the inconvenience of having a bunch of USB external SSDs floating around, especially since none of them are large enough to backup my entire drive if I get close to filling it.
I appreciate the perspective, I definitely take backups seriously for my photography.
I think a combination of:
1/ ZFS datasets with hourly (or daily) snapshots
2/ Samba with vfs_fruit
Gives the peace of mind that even when the sparsebundle shits the bed, you can rollback to a suitable snapshot and only lose a small period of backups, rather than having to lose the entire history and start again from scratch.
(I say when, not if, through considerable experience over the last 15 years that it will always, inevitably, shit the bed.)
A 2-drive Synology (e.g. DS225+) in RAID 0 or RAID 1 works fine for this, for 90% less than this beast. Synology documented their optimal settings for Time Machine a couple years ago, too. Hope this is helpful. [1]
[1] https://kb.synology.com/en-us/DSM/tutorial/How_to_back_up_fi...
Or if you want something from a vendor butting running decade old hardware configs and trying to lock people into their drive ecosystem, UNas or many other options.
Stay away from synology.
I already have a DIY NAS w/ 14x 14TB drives in it running ZFS on FreeBSD. It does not play nicely with Time Machine over the network though, and has some other bugbears that I've resolved to fix by migrating to Linux and running ZFS on Linux, but have never got around to doing.
A 2 drive anything is not replacing my existing NAS + solving my backup use case, although I appreciate the sentiment of saving money.