A true tireless "porter."
Installed in a Synology NAS with eighteen hours of daily operation (Read/write) in a RAID 1 configuration, it has been functioning very satisfactorily for months and is invisible in terms of problems, malfunctions, and delays.
It seems relatively quiet (perhaps the low rotation speed helps) whether it is idle or writing/reading, but since it operates in an array of six drives, I don't have an opinion on its exact noise level. In any case, it doesn't seem to add noticeable noise to the system.
I recommend it as a NAS drive for managing large volumes of data, primarily consisting of large files.

They are simply unacceptable at WD. I bought it from Plaisio and after 1 month suddenly it asks me to format it, with files for professional use. The disk was replaced. The second time I format it and realize that it was 2TB instead of 4 (it said 4TB on the outside). I took it for replacement and again the same thing. I was probably unlucky and fell into the bad batch.

Excellent disk for NAS, installed 6 in Synology DS1821+ without any issues for a while now. Note, because it was mentioned in the comments and to avoid confusion: The disk is a regular CMR and not SMR as mentioned somewhere. WD also states this in the specs. It fully replaces the EFZX. Only the EFAX is SMR and it is not classified as a Plus.

I have a pair inside NAS. The only thing I have noticed is that they are heard at regular intervals, as if the NAS is accessing something that was not happening with the corresponding 4TB ones that were replaced

Installed in raid ZFS, it is one of the 5 disks in the array. All the other disks are old and simple, not NAS. So it is the only one out of the 5 that shows errors, it needs resilvering at least once every 10 days. Fortunately, no data is lost (yet) and there hasn't been a permanent physical damage to the disk, so I can't even ask for a replacement. It may be more suitable for simple use. Get informed before purchasing it.

Initial impressions: it is difficult to hear it in continuous operation. The temperature remained at 33 C after hours of backup (of course with the help of a fan inside the HDD case). However, I recommend the EFZX series because it is CMR. Due to lower cost, SMR will soon be the only available option. As for reliability, time will tell.