Im new to LiIon, I dont have a lot of older cells, I dont have unprotected cells, and I dont rely on external chargers.

If a charger falls short of 4.2v, I consider that safer.
If a charger works too fast, I consider that less safe.

since Im new to LiIon, and 16340 in particular, All my cells have USB rechargeability. It is imo, the newbie friendly, more modern option.

Not to say that there arent plenty of old timers that do fine with chargers and unprotected cells… Im just conservatively cautious about LiIon use, and imo the USB Protected 16340 are a no brainer… No charger needed, whats not to love? These are not proprietary, that is, they work in ALL my lights, they are not tied to a specific light model, nor to a specific charging strategy.

The only proprietary battery mentioned in this thread is the S1R battery, which I do not recommend at all. Also this thread is specifically about the USB Rechargeable cells, it is not about IMR, or other chemistries, nor about non USB batteries.

I think the USB batteries are a totally viable option, and imo lights that include them make great gifts for newbies, who may not need to learn about chargers, voltmeters, and the safety strategies for using UnProtected cells.