Admittedly, you’re new to this stuff and therefore inexperienced.

Slower isn’t safe per se, it’s just slower, since cells have a charging range speced in.

4.20v (+/- .05) is the standard. Less isn’t safer.

With 16340s and PCBs, we’re talking generally ChiCom li-co chemistry, which is the reason you’re using a PCB in the first place. With modern lipstick lights drawing higher currents, li-co isn’t ideal for that application, since li-co is a <2A chemistry.

If you’re not running on high/turbo, all that often, then li-co can be fine and offer slightly more runtimes.

Anyhow, stick with what you’re comfortable with, but there’s more than one way to skin a cat.

Chris