It looks like a deathtrap.
What if you're taking a bend quite fast downhill? The child on the back could easily jacknife.
what if the child on the rear bike tries to steer? It could upset the balance of the whole thing tipping it over, sending everyone on the front bike flying into a river.
What if the child on the back detaches themself and inadvertently rides the wrong way or crashes and you ride for miles before noticing they're not there?
I wouldn't touch it with a bargepole. If you want your kids to cycle, there's only one method. Get them a bike, get them learnt how to ride it, and get them riding along
in front of you. No fancy metal attachments will replace that. This thing is obviously the brainchild of some bored person who can't think what to do with himself since being made redundant.
But presumably you'll decide that it's ok becaue it's been theoretically proven to be in some lab