They rock. They charge really fast (at least with this charger). If they malfunction they can catch on fire. They lose little capacity when stored. They're lightweight.

I have one P7 light and 4 protected 18650 cells. I labeled them 1-4 and swap them out after every ride, even if I don't discharge them all the way. The cells are light enough that it's not a problem to carry all the spares in my bag. On high that's over 4 hours of burn time, on medium it's enough to get me from sunset to sunrise. I wouldn't charge them unattended or subject them to extreme heat or cold.