'Quality', as it is used here, refers to better or lesser, as in 'this material is better quality (for a specific purpose) than that material'. Since there's no secret or special technology for producing 'better' all around vapor, I think it's misleading to use that term. Doing so promotes the myth that a high end vape can produce 'better' vapor, or a vape with an all glass path delivers better vapor. With all glass the taste may be better for some, but taste, like density, volume, and temp, are all separate attributes of vapor production, and each can vary from one vape to another, and even vary according to how just a single model is used. I don't think lumping all or even some of these attributes into 'quality' is a good idea, especially since most attributes of vapor are subjective, as far as good or bad. One vaporist may like high density vapor, another may not. A big hitter doesn't produce better vapor than a stealth portable, just more vapor per hit. Some will love the big hits. Others would rather sip.
I think we need to be specific about the different attributes of vapor production and delivery. 'Quality' is just too vague and potentially misleading.