It is a weaker flavor IMO, even though the color made me think it would be super strong. It mostly tastes like vanilla, but with something else... maybe caramel as Vappa said. It is not "buttery" though it is sweet; not as sweet or vanilla-y as some of the french vanillas I have tried.
I made a standalone mix at about 12%... it was good, but not as good as I had hoped it would be. I would not be unhappy if this was my last bottle & I had to
vape it all day. I predict it would mix very well with: dry tobaccos, nutty flavors, "bread" flavors, coffee. In most instances, I predict you would get a better result using a simple mixture of good vanilla and good caramel. However, vanilla butternut can do this in one step instead of 2 or more; I will try adding sweetener, I think that will improve this flavoring greatly. For those who like vanilla but find most flavorings TOO sweet, this is right up your alley.
On color: this is a very dark flavoring, which gave me concerns, especially after the similarly-hued LorAnn black walnut destroyed my carto upon entry. Having put about 10ml of my 12% mix through a carto
tank, I have not noticed any irregular or extreme degradation. So far, vanilla butternut does not appear to be a carto destroyer.