I’ve got some round eBay ones … if you remove the bottom mount and screw onto a bar mount of some sort they are nice and firm and not at all bad for casual riding.
I had a spare CX dropper lever that I just made into the bar mount for example and the batteries fit inside an Nescafe Azera tin which also just happens to fit in a bottle mount. Battery life is fairly shit though so I’d take 3-4 batteries out for a couple of hours.
This works really decently but even better if you ride with mates with decent lights.
The real difference though is like dirkpitt say’s… if you then decide its a huge amount of fun a proper set of lights completely changes things.
Before last year I used to think people were bonkers cheering the night drawing in… then I tried it and spent my life savings on lights… it’s totally NOT what I expected… its way more fun and way less scary than you think it will be.