There are a ton of HD action cameras on the market right now following GoPro. Most of them are not really worth looking at but Judd actually think that the Xiaomi Yi HD brings a decent offering to the table which can compete to some degree with the GoPro especially when you keep in mind the low cost.
As long as you are O.K. with having no screen at all (everything is done using wirelessly from your phone) you can enjoy pretty decent 1080p quality video. Yes there is not a lot of control over the image which is kind of a bummer but for the target audience it is not a surprise.
It is worth mentioning that Xiaomi does have a new 4K model which should reach the market (globally) soon. Some units have already reached some costumers recently and you can see a video comparison of the Xiaomi Yi HD which Judd reviewed next to the 4K version: