I was part of the development of this helmet, so will give a bit of input from my side.
Firstly, the helmet was developed in coorporation between Rudy Project and Team Bahrain-Victorious (not SwissSide). I was the leader on Team Bahrain-Victorious’ side of that coorporation and was involved from the start of the project.
There was a question of why this is marketed as a TT helmet and the reason is that this was developed to work best in what I would call a modern TT position used by most (fast) professional bike riders. It’s not to say it won’t work for a triathlete, but there’s a bigger range of positions (from top pro to BOP AG’er) and (like with any helmet) this will not work equally well on all. When making the general shape of the helmet it was a priority to not lock the design into one very specific position/rider, but it is still optimized for what you could call a modern TT position.
After finishing the development we have tested it in even more positions (even on a road bike position) and actually found that it performs really well in most instances - even ones it wasn’t specifially designed for - but of course still have positions/riders where it excels.
Regarding the change of visor, it will likely be made a little bit shorter in order to make it easier to drink from a bottle without having the bottle interfere with the visor. I personally tested this slightly shorter visor and found no aerodynamic difference to the original/taller one.
Regarding general sizing, both sizes are the same size outer shell so it’s only the inside that has a different size. So choose the size that fits your head and don’t worry about a difference in aerodynamics 