The correct binding depends on your size and your DIN setting. I have both the Free-Flex 15 and last seasons Free-Flex (hmmm, 13 or 14) on my skis. (Different pairs of skis.) There is also the Freeflex 17 which has a higher Din range.
The Free-Flex 11 has a lower DIN range and some people refer to it as a "Junior" binding for that reason and because it does not have as many features as the 15 and 17.