Nice affordable mini server. Definitely room for improvement though. The software is buggy, with little to no documentation on how to figure out all the settings and options. Build quality is solid. When streaming from other devices, sometimes the connection will randomly drop. For whatever reason, the operating software doesnt like playing MKV files and will randomly stop streaming the audio layer, so your left with video playing without any audio. For best results, convert any movie files to MP4's and this will play it with no issues. Shows up on all my devices as a media server without any issues. I do like this product, but with a little more improvement, this has the possibility of being a great mini home server.

What I use this for:
As the target for file history on my Windows 10 machines. Works great. Image backups themselves always crap out for some reason. I can browse my main computer files (the backups) even when it's left off, remotely.
As a Web server for a small personal website via NoIP.com, works great. The NAS's update app for NoIP works fine.
To hold music and video files and serve up to everything including tablets/phones, works great, especially for Fire TV (with a DLNA client app).
As an OwnCloud server to provide instant upload from my phone camera anywhere, and keep (literally) my own cloud for syncing important stuff between devices.
As an FTP depository for a webcam.

PROS: Easy to set up, Web/FTP server works great, Media Services work well, has not crashed or had any technical issues in the last year, fast enough to stream video to two tablets simulataneously (haven't tried more). This needs a solid network to work correctly, I didn't even achieve its full functionality until upgrading my router to a WRT3200ACM. It is reliable (1+ years).
CONS:
No encryption, just the share/user access control. The processor couldn't handle it anyway, it reduces backups to a crawl (they don't work anyway).
After losing my public IP, I am pretty much hosed. The Zyxel Drive app connects but always hangs when trying to get anything. It is perfectly serviceable to access your stuff remotely IF you have a public IP via web/ftp/webdav, however the Zyxel cloud apps are garbage. I am currently using softether to VPN in to a home computer but it is abominably slow.
UPnP setup talks to my router but says ports are already in use and requires remapping. Easier to just DMZ (potentially dangerous) or set up forwarding manually on router.
The fan is silent but doesn't move much air or seem very responsive, drives run HOT at 60C with the cover on and 50C off.
It does vibrate (probably can't help it with 4 drives), some rubber furniture feet have helped keep it from being noisy on the wooden shelf I have it on.
The processor is SLOW and the interface is not quick. Actually serving files seems an appropriate speed, 100MB/sec across the network.
The OwnCloud client is older but works quite well, there have not been any updates in quite a while. However, it hides the OwnCloud data directory inside a non-accessible system directory. I managed to change this via WinSCP and the configuration file to a normal share, but you will still not be able to access/backup your OwnCloud other than through the client on another computer.
The biggest flaw is a garbage backup application. I initially thought it would super easy to backup the RAID to a large external. I have never had a backup complete to an external or internal (prior to using all 4 bays for the RAID) drive, and certainly wouldn't trust it to ever recover. I back this up using WinRAR on my main computer which is tedious and obviously not realtime. The lack of any new packages to backup to a cloud service is pretty much disqualifying in 2018.
SMART flags do not notify you in any way--I have one marginal drive I have to keep an eye on manually.
The SSL certificate stuff is totally incomprehensible. I bricked mine and had to restore from a firmware settings backup. It's not much of an issue for me other than a new computer has to install the default certificate or you will constantly be getting the browser bugs that the certificate is expired/invalid, bad if you want an HTTPS website or to really lock it down for public access. HTTP works fine, but then your only firewall comes down to your admin password, not great. Your share permissions become critical here.
To sum up it's been a largely good, not great machine. It's features and abilities are decidedly obsolete though, and given the expense of the HDs it's hard to recommend this when so many newer models do more stuff.

This is an effective home/small network NAS.

When initially readying the trays to receive a drive, you have to separate the side connectors, and you feel like you might break them, but they do pull away cleanly.

The first drive initialization took a bit longer than I expected. I disabled the Twonky server, as it didn't fit my usage needs. It performs better with that disabled.

The USB 3 read/write speeds for external media is slower than I expected.

Overall, this is an effective device - I was looking for a lower power solution than leaving a full PC powered on at all times for simple home network storage. This item fits the bill.

2017-08-11 Update:

I've now had this NAS for a little over a month. I loaded it with 4 WD RED NAS 4TB HDD's and put them all in RAID5. The process of installing the drives and setting them up on the NAS is very simple and straightforward, including RAID configurations.

Note: If you're planning to do load yours with similar drives, remember that a HDD's advertised size differs from the actual recognized disk space (in short, this is due to a difference in how HDD manufacturer's report/measure bytes (1000) vs how computer systems do (1024)).

Back to the NAS: After getting the disks set up, I started configuring various functions and features of the NAS. I added shares, users, and set which users/groups had permissions to each. I specified which folders and what content type would be published to the media server. They have the media server configuration basically predefined and preconfigured leaving a computer-savvy user like myself slightly disappointed with the level of control available. I set the network settings, host name, DNS configurations, FTP, WebDAV, etc. and configured all to my liking. I investigated features like the sync button, which allows you to copy content USB > NAS or vice versa. Everything I tested seemed to work really well.

I predominantly bought the NAS to provide a lot of easily accessible storage with RAID5 protection so that I could stop using 6 different external HDD's and just have one repository. It works excellent for this purpose, but another feature which I am really getting a lot of use out of is the media server.

The device makes itself available on the network as a media server. Basically any other Twonky server, Windows Media Player, AllShare, and similar services will see it and be able to browse it. For my Samsung Smart TV, I simply change the source to the NAS and browse its contents, allowing me to quickly find and play something. Alternatively, on a computer or fully featured browser, I can go to the media server page, find content, and then play it right in the browser or connect a player like VLC. I can also find content in the browser and then cast/stream it to the device of my choosing (it shows which devices can accept a stream). It works really well. And if you use the computer, you can add media to a queue for a device you're casting to. I had absolutely no issues simultaneously streaming three separate HD movies to three separate devices; I bet I could do more. One thing I don't particularly care for is the support of thumbnails or pictures. So far, it would seem only MP4's show a thumbnail of the video. Thumbnails are not generated for content types like AVI or MKV. The thumbnails are helpful when trying to find something to watch. This isn't a deal breaker and I intend to research Twonky a bit more to see if there's a way around it, but it's worth noting as some of you may be more casual users than myself.

There are a number of features I'm not using now and am not too likely to use, at least in the near future, but it does what I need it to (offer a lot of storage protected with RAID) and then some (media server, download service, sharing), and it does it all well.

The last thing I'd like to point out is unlike the experience some others have had, the Twonky Media Server is very quick for me, easily shows all results on a page, quickly switches between video, photos, and music, and reflects changes to media files with nothing more than a refresh. Expanding on what I described before, I've had zero performance issues browsing, finding, and playing content from it on three separate devices simultaneously. I haven't yet tested the cloud feature, but intend to soon.

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I purchased a Zyxel 2 bay NAS for work for testing and was really impressed with it. It inspired me to buy (a larger) one for home, so I went with the 4 bay.

Initial set up was sort of tricky on a corporate network, but fine at home. I haven't yet configured or tested all the features at home, but considering my experience at work, my expectations are high.

I intend to update this review at some point to shed more light on it.

Fast performance, easy set up interface, It took a little bit to get started but that is mainly in the getting used to the user interface. Finally got the 4 drives to run this device at the full RAID5 setup with 4x 3Tb 7200RPM drives. The RAID creation process was surprisingly short for this volume. It only took about 15 minutes to complete. System firmware upgrades are easy and can be done directly from the web based Admin interface. I did have some trouble initially copying data to this device, but it was later eliminated to be a suspect router. Diagnostic / status lights are clear and easy to read. It is now time to give it the stress and usage test.