Thanks for the impressions - this, among other things, prompted me to go for the 213j (and a 214se for dad)! This is the successor model if I'm not mistaken.
The 213j is definitely quiet as well, the fan is smooth and introduces only a whisper of fan noise into the workspace I've deployed the unit in. Once I can move it further away from the PC the sound will undoubtedly disappear - I cannot hear it when walking up to the computer, only when sitting down.
I have a 3 TB Red (WD30EFRX-68AX9N0) and a 3 TB Seagate NAS HDD (ST3000VN000-1H4167) in there. The Red is inaudible at all times but the NAS HDD has seek noise. Very muted and soft compared to my AAKS, however, so no bother at all when working. The HDD cage structure was half-open, but it seems to handle these drives quite well: the case stands on rubber feet, and no vibrations are being resonated by my PC's Define Mini case. I wasn't sure what to expect because the unit's case is mostly plastic, but they've done a really good job even noise wise!
Getting the unit to run and RAIDing the drives couldn't be easier. The software is way more intuitive and responsive than the Buffalo stuff I've been using in the old NAS. It's like it's a proper OS or something...
Definitely excellent bang for buck if you want to do more than just plug a drive in over the network.