Just got mine. Here's the deal (IMHO of course, I'll leave the science to the more qualified.)
Very good vapor, dependant on the power source. On 2 desktops, great, very much like a 95% battery. On my really crappy laptop with a PCMCIA USB adapter, more like a 60% battery. On my Black and Decker portable power supply, also about 95%.
The pressure switch is fantastic, very easy draw without being hyper sensitive. Does not appear to have any sort of safe feature to prevent you from overheating your atomizer, so watch out Leaford! The switch is comparable with the better batteries I've had. I keep thinking however, that this may end up being the weak link. I hope to get 9-10 months out of it, but that may be over-optimistic.
The led is pretty cool. Very deep red, and sort of a star pattern around where the cord exits the end.
The unit feels very solid overall. Cord is very flexible (a plus for sure) and light (ditto.)
If you want to save your batteries for on the go, this is a great way to do it barring any long term reliability issues with the switch.
BTW - Mine is the penstyle model.