There were (are?) at least two variations of the two piece pulley. One involves a "dog clutch" arrangement where the sheave and hub pieces are held in engagement by the tension of the ratchet nut.
The other version mates the two pieces on a male/female thread, which is then held by the ratchet nut - which in my mind might complicate removal in the event of breakage of the v-sheave. Threads, as all threads are when exposed to the weather, are wont to "rust together." Which might complicate your removal if the sheave breaks off at all arms (or even if it doesn't.) This would bring removal into the realm of a pipe wrench - or removal of the hub portion anyway. Which sort of puts this two piece variant back into the level of difficulty of the one-piece.
I have used both one piece and two piece dogclutch, might prefer the dog clutch type for the "on the road" experience should it occur, but have never had either version fail.
Joe K