I got some of the non-rechargeable lights for about $1 each. They would work for a week or so, then time to toss and get the next one.
One issue was pushing them until they got far too dim to actually be safe. Also, sometimes they might get bumped and go off.
Still, not a bad thing to have on hand to hand out to needy cyclists.
Anyway, if you need lights a fair amount, go rechargeable.
I've used the CREE lights with 8.4V external battery packs. VERY BRIGHT, and interchangeable batteries are nice. Unfortunately, one has to strip lights from bikes otherwise they get stolen. So, they're a pain to put on and take off. And, inevitably I've had issues with them. One switch got mashed and became non-functional. I've had a couple of cords pull out. That kind of thing. Also lost a couple of battery packs.
I've had cheap taillights that would also randomly fall off.
Still, I've had issues with mainstream lights too. The charging port wore out on a $100 headlight. Also my very expensive Fly 6 busted mounting straps (and the company refused to sell just spare straps). And, also eventually stopped taking a charge.
I've got a couple of other lights that I need to try out.