+1 for the gvg. A bit pricy, but amazing when you learn how to utilize it. I personally think those liquid concentrate pads are a must. (I still need to practice my technique with it though.)
That burning taste/smell is common if you apply too much heat. Spice has a pretty low boiling point, and there's a little learning curve to properly vaporizing it.
Purity is a concern many others have too. There are lots of good resources here to help you feel more comfortable about your spice. Wouldn't hurt to look into it, but I think your problem is just too much heat. If the purity thing scares still you after doing some research, you can always toss that product into a new batch to run through another extraction cycle.