I recently had a few customers who were really frustrated. They bought what they thought was an MHL extension for their S4 or Note 3, only to find out that it didn't work when they tried to connect it to either their SmartDock, or to their MHL adapter. They had bought the Model: 4XMHLADAPTER called the "MHL Adapter Cable for Samsung".
So, I decided to purchase one of these cables to try it out myself. After all, it sure looked like the cable that we built. What I found is that it looks similar, but it's not fully MHL 2.0. The male connector is MHL 2.0, but the female is MHL 1.0 (aka, USB Micro-B). No wonder it didn't work with the MHL 2.0 items. In fact, I don't really know what you'd use this cable for - there's really no reason that I can think of to use this adapter.
Here are the female connectors from both. Ours is on the right, which is why it's compatible with the newer Samsung phones and MHL items, like the dock and the MHL cable.
If you look closely at the picture above, you can see that the one on the left is flat at the bottom, that's the MHL 1.0 version. The one on the right has a notch in it, that's the 11pin MHL 2.0 connector that works with the newer Samsung phones, such as the S3, S4, and Note 3 (and probably beyond as they continue to make new phones). FYI, it's not just for Samsung devices, it's also relevant for those of you who use the Pioneer AppRadio - so take note!
Here's a link to our MHL 2.0 Extensions: http://www.usbfirewire.com/Parts/rr-mhl-ext-xxg.html
If you're wanting an MHL 1.0 Extension (think Galaxy S and S2): http://www.usbfirewire.com/Parts/rr-mcb-ext-xxg.html