A Firefly was one of my Xmas gifts, so I've had one for a little over two weeks now. I've held off on posting any kind of review, because I wanted to actually get to know the unit before making up my mind about it.
The verdict is that I'm really happy.
I was a little nervous for the first day I had it, mostly because I was reasonably happy with the portables I had (Lotus, Solo, PnP, DV as a backup) and hadn't really planned to buy another. The only reason I did was because of how much the FF reminded me of the Lotus (my overall favorite vape), particularly the potential to take single hits on-demand--which is important to me. As much as I love the Lotus, it's not great for stealth out of the house. I'd previously owned the Firewood, which I'd purchased with the same desire, but didn't really care for using it enough to want to keep it. While the FF is clearly a higher quality vape than the Firewood--and much heavier than I'd anticipated--I wasn't sure it was going to feel worth $250 to me.
After a couple weeks, however, the FF has completely replaced the PnP in my daily routine. It works a lot better for me because it doesn't take the pre-planning the PnP does, nor the maintenance. Not having to mess with bullets is a blessing! I'd love a better battery life, but the fact that I can even buy a backup battery makes it a relative non-issue. The FF is easy to load, easy to use, tastes great, and easily fits in my pocket/purse. I feel like I've simplified my life now that I'm using it when I would've grabbed the PnP in the past.
In response to some of the discussion above, I can't imagine how anyone has managed to get material in their mouths while using the FF. I've run the gamut of grind types in playing with this thing, from a whole nug to hand-shredded to medium ground to finely ground, like sand. I've varied my draw speed from barely an inhalation to a fairly steady suck, and not once have I managed to get anything green on my tongue. I'm not saying it's impossible, obviously, but anyone on the fence about purchasing one of these shouldn't worry too much about the possibility. This is honestly one of the simplest vapes to operate that I've come across, once you get a feel for how long to hold down the button while heating.
Overall, I'm really happy with this purchase to the point that I'm ready to narrow my collection again, since some old favorites are no longer seeing any use. Given the distracted, multi-tasking nature of my sessions, the FF is the closest to perfect battery-powered vape (for me) that I've found.