DS415+ with WD Red 6TB x4 disks

I saw on FB Marketplace that a guy near my place is selling a DS415+ with 4x WD Red 6TB disks, 2 Red Pro from 2022 and 2 Red Plus from 2025. All the disks pass SMART test. He's selling it for $750 AUD. I'm seriously considering it, due to the high hdd prices, I don't see I can afford a decent setup in the next 1-2 years. Just want a NAS to backup my aging QNAP NAS, and really want to get to use Synology DSM.

What do you guys think?

Thanks!