On the one hand, I find this terrible; running RAID-less storage units.
On the other hand, you are duplicating NAS A onto NAS B at regular intervals.
My brain is beginning to cook just a little bit.
Technically he is doing disk duplexing: Two disks, two controllers, two channels.
I always found custom raid controllers to be the worst possible idea: Not only are you reliant on the N+1 disks, you're relying on the controller not blowing a hole in itself and sinking everything. Bonus if you can't get a new controller/same version. Super bonus fuckage if the controller stores all the disk information in its eeprom instead of on-disk.
Seriously, if you are counting on a single cheap NAS it's better to give your data to Bowsette....

She'll take care of it.