The Elgato Thunderbolt 2 Dock is really useful for those that have 2011 Thunderbolt capable Macs or for those that just want a way to easily dock their thunderbolt equipped laptop.
The design puts three ports on the front (see pic below) and makes it easy to attach a USB 3 device, microphone, or headphones. I tested the front port's headphone output and while I was not a fan of it with revealing earphones (I tested it with Ety ER4Ps), it did sound acceptable with a pair of more forgiving phones (ATH-M50s). It doesn't compete with separate DACs and amps, but it works fine if you aren't picky about sound quality.
The power cable actually has the company's name on it, which I found unusually nice. I recently organized the cables in my office and found that most power cables do not have the Company's name. This makes it hard to match things up if the cable gets detached from the device (especially when you have several devices that have power cables disconnected). The other great thing about having a power cable is that you can use the USB port to charge devices even when the computer is off or disconnected. I recently added a Logitech mouse to my main setup and it needs frequent charging and this will make the process painless.
On the 2011 iMac, I was using the second thunderbolt port to feed an HDMI display via a Display Port to HDMI cable. This cable has had issues since I first starting using it. My second display would work fine for a few minutes, but it would either go black or go to complete static. It has made me stay with one display use most of the time. However, after I hooked up the Elgato dock via the same thunderbolt port, I tested the HDMI output with my second monitor. The connection was rock solid. I am going to get rid of the Display Port adapter and use the HDMI cable with the Elgato going forward. I recently discovered how useful a second display can be in Lightroom for browsing catalogs, so this came right on time. I should mention that Elgato claims that it works with displays up to 4096 x 2160 pixels of resolution, but I only tested it with a monitor in 1080 HDTV mode.
I also hooked up a 2011 MBP to the dock via thunderbolt. This allowed the iMac (which was connected to the other thunderbolt port) to be used as a second display (CMD F2) for the MBP (very useful since I have Win7 installed on the MBP for work). It also worked flawlessly. The Elgato comes with its own fairly short (1.6 feet) Thunderbolt adapter, but it came in handy and was the perfect length for this application since the Elgato sits on a mStand that is right underneath the MBP.
All in all, I am very happy with the device. It really is a perfect compliment to 2011 Macs (those with thunderbolt) and I will definitely get a lot more use out of my second display with its HDMI output. The device retails for around $200.