I've used the tongue method in tasting fairly often. It's not going to give the greatest sense of the juice in its entirety, but it can give you an idea of how it's progressing, although a "quick and dirty" method indeed, you kind of have to mentally "translate" the taste in comparison to how it may taste vaped. I mainly use it as a method to make sure nothing is horribly "off" with my flavors as I steep them.
I have never, ever tried a drop of flavoring straight, on my tongue. I assume the taste is "similar" to when my mom finally broke down and let me taste a "teaspoon" of vanilla after I nagged her enough.... A life lesson that will stick with me forever.....

And yes, I did it to my own kid, obviously. Sometimes you just have to let these "life lessons" occur. LOL.
Anna