I've seen some videos of people using and talking about them.
Apparently they say they're good if you find it eg easier to surf frontside on a shorter board, however you want something longer for backside.
I'm not good enough to be able to comment, but it would be interesting to know.
Replied on Hey Clayton Nienaber Have you put any...
17 Aug 04:42
John Dennis I suppose you could consider it to be two half surf boards, so you'd just shape one rail for frontside and the other for backside, but Clayton Nienaber would be have a better understanding.