I've known that CPF has existed for a very long time, but it wasn't until recently that I felt the need to stop by. In the past, my choices for lights were AAA, AA, and CR123A, and those served me very well, but the advent of the commonplace cylindrical lithium ion rechargeable lights and my desire to finally upgrade my lights for the first time since 2014 brought me by. There was a whole body of knowledge I needed to acquire about the new types, because in the past, I have always regarded rechargeable flashlights as less desirable for someone like me, a non-professional user whose batteries would be more likely to self-discharge faster than they were actually used.
And I've always preferred primary cells for that reason, because I know the spare cell I carry around in my handbag is still going to be near 100% capacity months later. But I found a use case scenario for the 21700 battery in my life, in this age of iPhones and iPads that I end up having to top up frequently when I am on the go, so I got one. Around town, I carry a 5200 mAh backup battery for my iPhone, and when travelling by train or plane (or for use during power outages), I have a 13000 mAh battery pack for both iPhone and iPad. Those same packs can charge my 21700 flashlight, or I can get a second 21700 battery and charging cradle and use that to charge my iPhone.
I have to say, I have always regarded flashlights as essential tools that everyone should own, and when I say "EDC" or "survival", I never speak about those subjects without talking about knives, flashlights, firestarters, and writing instruments, all in the same breath, yet it seems like there is no lack of interest in talking about knives, but not as much interest in talking about flashlights.
I can say that while I used to collect knives, I never collected flashlights, but the reason for this is that knives are, not to put too fine a point on it, a thoroughly mature technology, while flashlights are still rapidly improving and obsoleting older versions. The flashlights of 2021 are leaps and bounds better in performance than the flashlights of 2011, but I'm still carrying knives that date back to at least the early 1990s, when I first started to buy "serious knives".