I've had both Billow Berry and Sapphire, and didn't think much of either, but for totally different reasons (I do like BVC, but would like the blueberry to be a little stronger, and haven't tried Star Dust, but have always wanted to).
So, for me, Billow Berry had that BUT (bad, unidentified taste), that I think has something to do with butyric acid. It's a flavor that I just can't stand, but I don't think everyone is sensitive to. First time I tasted it was in NT's Creme Brulee, but I get it from Ahlusion's Fort Custard and the newly-reformatted (I'm pretty sure) Gold Member, as well. I just can't do it. Bleh.
Sapphire would probably be amazing on just the right equipment, but it isn't on mine. I find that maybe one hit out of five is just great, but the other four go between too weak and burnt. I think it's seriously temperature sensitive. The rare good hits are both sweet and tart, and very much a candy blueberry, but a GOOD candy blueberry. It isn't for me on my old-school tootle puffing set-up, but I could see it being very good on the right set-up for it. I'm just not willing to experiment with finding the right set-up for it, when I have so many flavors that work well with what I have.