I've never seen anyone use those. I guess its a simple way to quad line a 2 line sport kite, but there is a far better way.
Here's a couple of reasons why they will not work very well (compared to what I will tell you)
1 - Adding those flaps is going to radically change the way the kite flies if the lines attached to the flaps are tensioned at all during normal 2 line flying.
2 - Flying4 line using the normal 2 line tow points will give a much smaller range of AOA adjustment and on some/many kites I really don't think there will be enough distance between the flaps rear lines attachment points and the normal 2 line bridles attachment points.
I've put some instructions on how to Quadline a 2 line sport kite here, so it becomes part of the resources of the site and is easy for everyone to find.viewtopic.php?f=68&t=14258&view=unread#unread