I've been vaping unflavoured for a couple of months now. That is after I was told by people around me that I was creating a smell, and not all agreed that it was pleasant. For stealth-vaping (restaurants, airplanes, hospitals, theatres etc) I think it is essential.
I have learned not to use it in a new clearo, or a PV that has just been recoiled/rewicked as there is often an unpleasant taste as the device beds-in. (This is often the case for flavoured juice too, but unflavoured is much more sensitive). Also, if used in PV that has had flavoured juice through it, expect a slight remnant of that flavour to persist for a few refills - not unpleasant, but I am told the vapour is practically odourless.
I mix my own flavourless 70%PG/30%VG/18mg nic. It is very easy to do, and very economical.