Yes, I know GoPro is the gold standard among sport cams -- and deservedly so.
But I picked up this one, the CamPark ACT74, on a whim and I'm really thrilled with the results. The picture is terrific (and it's 4K). It's small (same size as a GoPro Hero 7), tough and works great underwater. And it's for sale on Amazon for under $50!
It also comes with a whole bagful of accessories, including mounts for bike helmets and handlebars.
Now of course I would never presume to say that a $50 Chinese camera is equal to a $400+ GoPro. But for not much more than I pay for a tank of gas, this great little value really is a terrific buy. At least in my not-so-humble opinion. Great for stuffing in your pocket for a trip to the beach or a waterpark.