This, I believe, is THE question of the 2001-2002 ski season!
No shop in the country is demoing the HH because Rainey, starting this year, only sells direct. Very few (only one I have heard of in CO) will demo the Linken. Maybe Professor (the Linken rep.) can let us know if there are more options.
I have skied the Linken, and will ski the HH early this year and will report back once I've skied both. The Linken is VERY solid (as in durable) and transfers energy to the ski very powerfully. The plate really works. The step-in really works, and is a great convenience when skiing with your alpine buddies. There is very little pressure felt from the spring on the boot - to some that is a plus, to others that is a minus. It's a great design. In our heavy wet Sierra snow, snowpacking is a problem on deep wet days, but I have heard it's not such a big deal where the deep snow is dryer.
I've studied the HH closely and am very impressed with its design. six screws will hold it securely to the ski. A 6" spring with a full 2" if travel will prevent bottoming out. No cable guides on the side to get mangled by your ski edge. A good built-in riser that allows one set of screws to go into the ski without requiring long screw lengths.
Most interesting is way the HH interacts with the boot. The adjustable cable guides give you the option of either a cable pivot point near toward your toe or back toward the ball of your foot, the former being great for touring and the latter helping to pull the ball of the foot down for more control while skiing. Also important and often overlooked in HH discussions, the cable runs UNDER your foot along the boot's sole, applying pressure to the boot sole all the way until it reaches the flat horizontal piece of hard plastic which is also pressed against the bottom o the foot and from which metal cables then reach outside your foot and up around the heel.
Because of the cables/plastic wedge pressed against the sole of the foot, and the short length of the sturdy-looking heel segment before it reaches actually pressure onthe boot, and the cables running very low and along the edges of the skis - because of all this, energy seems as though it would be transferred MUCH more directly to the ski than any previous cable binding - though probably not as much as a plate binding. To me, the biggest question is: how much more control does the added ball-of-foot pressure provide. This will, of course, require on-snow testing.