They're pretty unpleasant--from either side of the cigarette. Equity has approved brands/versions of e-cigarettes (including non-nicotine options) to protect the actors, and they do check to confirm that the show is using an approved version. I'm not aware of any codified policy on herbal cigarettes, though. Most actors would rather use e-cigarettes when the staging permits it, but there is a certain lack of verisimilitude that may make them undesirable. (They don't burn down in the way that a real cigarette would if they are used over a period of minutes. And they clunk when they hit an ashtray.)
