I've owned numerous GoPro cameras and numerous of these knock off alternatives as well. I consider myself an amateur/enthusiast videographer, and I use them extensively in action sports in extreme environments and climates so I feel pretty familiar with what they're all capable of. (for the record, I love them all, it's just a matter of using the right tool for your situation)
Bottom line opinon (descending price and recommendation)
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Attempt at quick explanation:
You can buy any number of $40 'action cams' that come in waterproof cases that do 1080p @ 30fps with average cell phone quality. You can also buy loads of newer $80 'action cams' that claim to do 4k @ 30fps & 1080p @ 60fps. However, none of them do. It's only 2.5k upscaled to 4k @ 12fps. And 1080p 30fps interpolated to 60fps. You can easily analyze the frame data (as I have done).
All the $40 cams are essentially the same, and all the $80 cams are also practically identical. LOTS of different names, but basically the same. The newest SJCam (the original GoPro knockoff maker) labeled 5000+ is the only one that's slightly better (all the 6000, 7000, 8000, etc are SJCam ripoffs, not SJCam), but the SJCam 5000+ is $120, so there is no reason to buy it since the GoPro Hero is also $120 and is significantly higher quality (don't believe anyone's quality comparisons, more below).
Any of these $40-$80 'action cams' will probably suit you fine if you just want to pop it on your head and catch a few shots (I'd recommend 2 $40 cams since the 'higher settings' on the $80 cams are BS). But think of it like a Polaroid vs. a 35mm camera (old school analogy, but valid IMO). They're not equal, regardless if they both can print a picture the same size. If a Polaroid of your experiences suits you fine, then you're set! If you want more,
you can do it for half the price of GoPro, but not less.
None of these other 'action cams' are 'GoPro Killers' except the new Xioami Yi 4K (which is why it is $250, not $80). The chipsets, lenses, sensors, etc. on $40-$80 cameras are physically incapable of producing the same quality image as higher value electronics and optics. On a tripod shooting still subject matter the image may appear comparable, but in motion while shooting moving subject matter it becomes obvious they can't keep up.
To use an audio analogy, people tend to act like GoPro is like unnecessarily overpriced audiophile sound equipment and the knockoffs are equivalent to Sony/Panasonic stereos. This is not the case at all. It's more like GoPro is like Sony/Panasonic stereos and the knockoffs are exactly what they are: cheap Chinese fakes you get at a flea market.
Beyond image quality is durability, build quality, and functionality. GoPros are essentially indestructible. I've abused many and trust them thoroughly. Every single part and component in a knockoff, and the manufacturing of it (and the quality control of that process), is the lowest of the low. That's how the price is reached. These are not coming out of the same factory, nor using any of the same parts. They all tend to overheat, and the battery life on all these knockoffs is tops 1 hour of use, which is 1/3 to 1/5 the time of a premium action cam.
This isn't an "Apple vs Android" opinion thing. It's physics. There's nothing wrong with 'cheap Polaroid' for many circumstances though, just don't believe any quality claims, and accept that knockoffs are cheap, disposable workarounds.