DS has a Likeabike jumper which is great, but it doesn't have a brake. I've seen you can buy one as an extra, but it's for the front tyre not the rear (as on the Islabike Rothan).
Can any cyclists out there tell me if a front brake would be ok or would it be dangerous? DH seems to think it would cause DS to take a header over the handle bars. I'm no cyclists, so have no idea.