Summary: I've worked with several different QNAP units and while they are great little units this one is a bit under-powered, if you can afford a TS-259 instead of this unit I'd pay the additional cost. The power of the dual-core Atom, dual NIC, and expandable memory is worth the additional cost.
Summary: I bought this NAS a year ago for home use with two enterprise disks for mirroring. The device seems working as it is supposed to do. But one of the anti-feature is the USB One Touch Copy. It never works as expected. I wanted to backup all files to a USB drive in case the NAS crashes. After contacting QNAP, I was told that users need to add every directory/sub-directory names to the folder list for the job. It is not feasible for normal users.
Summary: My main goal, admittedly, was to get a NAS with an Operating System that was feature-rich enough that I could log into it directly to do some admin and maintenance tasks. This NAS looks to be running a flavor of Linux and supports ssh. I had no problems logging in, mounting/dismounting external drives via a USB 3.0 external drive dock, copying files from them to the NAS, fixing file ownership and permissions, etc.
Summary: Bought this NAS for the GDrive sync capacity. This app is deeply flawed. It was constantly deleting the wrong files and it ended up setting up folders upon folders of nested deletion files. I had to purchase an alternate solution.
Summary: I purchased mine with a pair of 3TB Western Digital HDDs. Installing the drives is a piece of cake. The Qnap automagically sets up a RAID1 volume the first time you fire it up. The instructions are clear. Be aware that the feature that allows you to access your data remotely over the internet doesn't work if you have Time Warner Cable and you use their preconfigured WiFi.
VMWARE & iSCSI feature set is incomplete / poor support
D. W. Corcoran "b393capt", Amazon
16 May 2013
Summary: I find the product lacking in its redundancy feature set and customer support. This comes from first hand experience during the failure of a drive in the QNAP TS-879U-RP, 8 drive product, in January 2013. I am writing to update this review in May 2013. My issues are not solved. In addition, what I had believed to be a VMWARE VMOTION issue, VMWARE has been able to reproduce and has communicated the problem is with QNAP firmware issue that isn't solved.