The thing is I already had the primo preamp in the chain, when I got the nu-vista 800. I was trying to sell the primo when the bike opportunity appeared. Never looked back.
I can tell you that the alps pot in the primo was a more linear volume control than the one in the nuvista.
That said, the word that got stuck in my memory to describe the nuvista sound is: fun. The nuvistor sounded different than a traditional tube stage.
I hope you are having fun with your nuvista as well.