Pros: - Setup was so easy, your grandmother could teach my grandmother how to do it.
Seriously, you can get this for a non-techie and they won't need your help. I don't know if I've ever said that about a NAS before.

- The web interface is really slick and extremely well-designed. The only better I have seen is on much more expensive Synology NAS units, however the Western Digital's is simpler.
As an experienced software developer myself, I am not easily impressed -- and I'd like to nominate WD's web interface team for a medal.

- You don't need to attach any annoying rails or special screws to each hard drive.

- The unit feels solidly build, is very quiet, and appears to use good quality components including WD's own Red line of hard drives, of which I have purchased dozens for various projects. I took internal photos showing WD uses solid-state capacitors (which last much longer and handle higher temperature than ordinary capacitors), but I cannot yet post images to a review.

- Link aggregation (use of two network ports for reliability) works with my HP ProCurve switch. I can unplug either cable and the unit works fine.

Cons: - Doesn't support 2.5" (laptop-sized) hard drives without an adapter.

- Only comes in black.

Other Thoughts: The initial review unit was damaged, but true to form, Western Digital took care of it.

I've used and configured many dozens of WD Red drives over the years and have experienced exactly zero failures.

With two hard drives, you have the choice between 6TB of storage space with full protection against a hard drive failure, or 12TB of storage space with no protection against a failure.
For most tasks I think the 12TB mode is just fine. Hard drives are very reliable these days. If your data is really important, you need to make backups -- the 6TB mode cannot protect against accidental deletion, fires, etc..

Pros: -Compact design
-Simple setup (provided you know what configuration you want)
-Straightforward browser-based interface
-Simple HD swap, when needed
-Ridiculous number of options (SAMBA, FTP, DLNA, Cloud, etc.)
-Detailed, well-written user manual

Cons: -Not so much a con as something to be aware of: If you have ever have to return it to factory settings, make sure you allow for ~16 hours. At least, that is how long mine took.
-Minor Con: When I plugged in my Seagate Backup Plus Fast 4TB Portable HDD, it didn’t recognize it, even though it is in a standard format (NTFS). The Seagate is, is essence, a portable RAID device and isn’t recognized by all PCs/devices, so it may be an issue that will be ironed out in a future firmware update. It sure would have been handy to transfer the data from it as opposed to transfer via LAN.

Other Thoughts: It was a fun ride getting this device set up to see how much load it could, in theory, take off of my main Windows-based server. My current server is a Windows 7 Pro computer which I use as a media server for 4 media PCs, DLNA server, a web server for 2 websites, print server, FTP server, and, at times, an HFS server for browser-based file access. If you are already aware of what the Western Digital EX2100 can do, then you would know that it can take care of 4 out of 6 of those features. I currently have a little over 4TB of data and so I decided to configure it as RAID 1, to see how it performed in mirroring mode and have been pleasantly surprised in the areas of ease of setup and performance. My main usage on my home network has been to access the audio & video files via SAMBA mount. I have a robust Gigabit home network and regularly test my local LAN speeds to my media server using Network Speed Test, which averages speeds in the 750-850Mbps range. For the purposes as described, this device performed fairly well. But, it is not going to replace my Media Server in any real way. I’m sure there are exceptions, but I have always perceived NAS devices as an “Average Consumer” device and I cannot see myself using one on a full-time basis in the near future. I can see the draw from the standpoint of a user who wants a feature-filled device that they can load & configure without much in the way of time commitment. I probably like configuring tech more than most, so that isn’t a selling point for me. As far as anything approaching a value, I am not seeing it at the current price of $750. The current price of two 6TB NAS Hard Drives is $540, so I would be paying a little over $200 for what amounts to a microcomputer that performs a few specific tasks, albeit fairly well. The device does what it is supposed to do and does it well, but my egg rating is still 4 stars because the value isn’t there, to me. This is mainly because I am not personally interested in this type of device, a reason for which I don’t typically ding a product for, but I did here.