A both of those still don't have the image quality a higher end GoPro does. They're close and a lot of people won't care - but a lot of people also do.
Yeah, I have a Yi and for the price, I think it's great. I'd like better quality but I'm not sure paying the extra $300 is worth a maybe 30% increase in quality.
I don't have a GoPro. I've looked at comparisons online. The Xiaomi is not visibly "softer" than the GoPro, AFAICT. Its low light performance is not great, but again, I don't know how the GoPro performs in low light. In any case, at $90 online, it's okay if it's a little below the GoPro in terms of performance.
The Mobius ActionCam is surprisingly sharp for its price and size. But it's only 30fps and therefore quite choppy. Also has a bit of rolling shutter. Here it is riding an RC car and a model rocket. I'd say it's good enough for that sort of thing.
