I just don't follow the logic of having to put smoke through your sinuses to get full flavour. Absolutely, I'm not saying what you should or should not do, because ultimately, I don't care. We can only speak from experience, so I'm merely sharing mine for those who are considering it, because it does differ from the fans of the practice.
When I smoke, I do not plug my nose. Same as when I enjoy the flavours of food. In both experiences, it is very fulfilling. Of course you will taste neither well if your nose is plugged. However, since my nose is not pugged while I smoke, I am able to get an incredible range of nuanced and interesting flavours from the mouth alone without bombarding the sinuses with a massive flush of tobacco smoke.
I have tried the snork/retrohale and all I am saying is that in my experience, it is not necessary to achieve the same flavour. In fact, I get MORE flavour when not doing the retrohale, and it is longer lasting. Obviously, we all have different experiences and preferences, and I do find the experiences of the retrohalers here curious. Perhaps I am one of those "supertasters", which makes it unnecessary to retrohale. Who knows.
Some people enjoy cigarette smoke in the lungs for that "lung feel". The sinus cavity flush with smoke seems like a similar thing to me, although I know many will disagree. Which is fine.
However, if there is any concern about health (a personal preference to be sure), the sinus cavity is without a doubt a very sensitive membrane and I think you are fooling yourself if you don't believe that there is a higher risk than average by flooding it with known toxic chemicals and carcinogens. Sinus cancer is a nasty thing, so all I would caution is for people to make an objective taste test before jumping into it with both feet. For me, I wound up tasting less on the retrohale. Your milage may vary. To all you confirmed retrohalers - puff on!