I think the advantage to the 3 axle trailer is the extra axle is closer to the center and helps getting over hills before the trailer snags on the hill.
I'm disappointed the new trailer is just another High Saddle 5-Slot. Why not give us a 6--Slot? Why not give us a decent 4-Slot. Step-Deck, Flatbed, Wide Flatbed, Sideboard, we already have so many 5-Slot trailers. What was the point of even adding this new one?