If I've got it straight there's 3 TT foils that have been released in the last month or so. This one is a straight go either way, bolt to the middle of your existing TT. There is another where the foil slides from one end of the fuselage to the other. Then there's the terrible looking inflatable board one.
I'm not convinced on the physics of whether you can achieve stability running 2 main wings, one backwards.
If you can, I'm not convinced of the benefits... except of course bolting straight to existing TT would make it a bit cheaper.
Looks like these bidirectional foils have a long way to go. But, early days. They will either improve or die a natural death. Good on people for having a go. Early kiteboards were pretty bad too.