I just ordered a sample bottle of Holy Vanilla!
Does anyone know what the recommended percentage is?
It varies, like most vendors, but I will say from testing about 10 of their flavors, I'd start at 5% on a 5ml sample bottle of whatever blend of PG/VG you prefer. This way you're not wasting flavoring or supplies.
To give you an example of what I mean by varies, I'll use Sugar Cream. More than 2% and it's overpowering and will dominate most anything you can mix. It's potent to say the least. On the other hand, Pound Cake she recommends up to 20% (directly from a post here in her own forum). I tried 10-15% and it's hit or miss. I don't feel it has a true pound cake flavor (missing the cakeyness) and comes off more creamy and potentially slightly buttery.