HDDs for NAS? SMR/CMR/ZFS?

I’m looking to buy some HDDs for my NAS, but I’m a bit confused about what to get.

I’ve seen people say “buy WD Red drives” because they’re built for NAS use, but I’ve also read that some Reds use SMR instead of CMR, and I’m not sure what the difference is. I’ve also seen mentions of ZFS, and I don’t fully understand how that fits in.

I plan to run some form of RAID for redundancy, but I’m not sure which drives are the best choice for long-term reliability in a NAS.

Can anyone explain the CMR vs SMR thing, whether ZFS matters for drive choice, and what I should look for when buying NAS drives?

I’ve found these drives from Cex, they sell quite a few variants and have good warranty, and tbh are more affordable that buying brand new ones.

2tb HHD link:

https://uk.webuy.com/product-detail?id=SHDDWDREDWD20ERFX2TB&categoryName=SATA-HARD-DRIVES&superCatName=COMPUTING&title=&queryID=8129B05C02060730E84C14D8CB5BFEC9&position=2