At the end, it's really a matter of where you are when asked upon.
If you are outside, the questions you encounter will be usually from curious individuals who wants to know about the
device. You can reply with almost anything, as longest you can explain what it is. I doubt that anyone would call the police just because you reply it as, "It's a personal vaporizer".
However, it's completely different if you encounter someone while using it
indoors, then you will be most likely facing an individual with a negative mind with responses similar to: "Hey, you are not allowed to smoke here". In this situation, you must come up with an answer that includes the fact that it's legal to use in order to avoid further frustration.
I think sellers should not make any claims saying that it is legal to use indoors. Because at the end, it's really the decision of the property owners.
E-cigarettes do have an aroma, and it does produce vapor that can possibly set off fire alarms. Exhaling any sort of vapor
indoors really conflicts a standard human logic and could have a negative impact on how the government will view such
devices in the future.