Wow. I'm speechless. I have three kids who've all ridden with me since their legs were long enough for their feet to reach the pegs. Crashing on that contraption and watching my child fly around those bars, or getting an arm or leg ground off when it gets trapped between one of those bars and the asphalt doesn't sound like much fun.
Also, and I'm quite serious, one of the joys my kids had in getting rides to and from school on my bikes is the "cool" factor in having their friends see them on a bike. I'm afraid this contraption only offers a DORK factor. If I want a cage around my child, we'll take my '79 Alfa Spider.
Anyone concerned with safety would approve of this device 100%. I think California would be the perfect testing ground for a law requiring this device on all motorcycles by next year. I'm sure the helmet law crowd agrees with me on this.