Technically, each model in the ZMF lineup offers something different and unique enough (while still being relatives) to warrant owning each.
Whether it’s something you can justify is totally up to your ears and wallet.
If you want a more “neutral” presentation, the Auteur is one of the best in presenting things very naturally.
On the other hand, the VO may be the most “unique” in its presentation. Have you ever listened to the VO out of curiosity?
In some ways, it’s similar to the Caldera (speed and details), but still quite special in other ways.
I may be in the minority, but I actually prefer the VO over the Caldera, for overall musical enjoyment.
There’s something amazing about each and every ZMF.