When I saw this thing for the first time a couple of days ago, my thoughts were along the same line as AW's. This design is demanding a whole lot of a single joint underneath the bottom bracket, but because it's a conversion kit it can't depend on any consistent qualities in the bike frame at that point.
Think about it. The kit attaches to the bike at only three places, and two of those places are the fork tips that have to turn for steering. So most of the torsional force transmitted along the beam of the load carrier must be taken by the bike's chainstays-- a part of the frame that's often damaged just by attaching a kickstand.
I can think of ways to accommodate different planes of rotation for the fork tips of different bike frames, but all of them reduce the rigidity and integrity of that point of connection.
It's a very cool idea, but I'd be surprised if it doesn't turn out to have major problems, like the kind that seriously damage your bike's frame.
Wish I'd thought of it. 
