Yep, the link is the little rectangular tab. It connects to four different places:
Each link connects one hex to the next:
It should be noted that when hexibrix are linked, they cannot be pressed onto a baseplate. This design allows for creating a board, specifically made of hexibrix. Using the various colors that are provided, you can easily create a hexibrix landscape.
The hexibrix can also be pushed onto a baseplate like a regular piece.
You'll also note that I stacked one on top of the other. It fits just like a normal LEGO brick. It should be noted that you will either need to align a 2x2 round plate on the first one, or you can remove the disk altogether. Either way, this allows you to stack these to make varying heights.
Below is an example of building a stepping stone in a river:
The example above shows just one example of using the hexibrix in conjunction with a LEGO baseplate. By forming terrain this way, you can completely negate the need for a hexibrix link.
I personally find the links good for establishing squads:
As far as the overall stability of the link, it is sturdy enough to keep the hexibrix together, but not remotely as sturdy as a standard stud-based connection.
Hope this answers your questions!