comments:
I don't know the general consensus around here regarding DAS over NAS, but I am a storage engineer in the real world and these all in one NAS boxes are appealing, but I would prefer to have a stupid box that i can throw an easily upgradable/swappable pc on top of and run TrueNAS on that. If you buy a fancy all in one NAS you are potentially tying yourself to that box and company for the life of it. Aside from advancements in cpu/ram etc, you have to worry about companies getting greedy and forcing disk manufacturer restrictions, or cloud data subscriptions that may show up on a firmware update a few years from now. At home I have this Terramaster 4-bay DAS (https://a.co/d/07GC1Uy5) ...under 200$, attached to a cheap lenovo mini pc i got on ebay running Scale and a z1 RAID. I would rather have capacity than bells and whistles. Since you are already controlling a NAS with just a Pi-4, I think this is probably a smarter move for you.
For my NAS I got one of these HDD enclosures and setup TrueNAS on a MiniPC which works great. Four drives, RAID 10. Just went to diskprices.com to get cheap deals, though prices have gone up a lot in the last year.