Hiya Adam, I broached this subject about the frames some time ago but didn’t get a bite from Flow.
My understanding is that there are only 2 generations of F frames, founding and now. Correct me if I’m wrong Flow.
I have harvested from both of the above and find little difference between them but I wouldn’t expect much as there’s already +10 yrs r&d in them.
I have found Flow to be very accomodating and I’m sure if you emailed them they would help you out price wise. 
It is disappointing seeing the US$ cost with Au$ discount in the same add but I guess their market is the US of A. I wonder if the new import Tarif will affect the price like our other US exports. 
Oh golly did I just get political? Shame on me.
Sorry.