I already wrote a review but somehow it does not show up. So, this is my second attempt :)
I'm quite happy with the XiaoCai X9S and think for this price it is hard to find a better cellphone. Extremely good value for this price. I'd buy it again.
Display: very good, I'd say the viewing angles are slightly better than the iPhone. The resolution is sufficient enough for its 4,5".
Style: I got the red one (which looks more like pink) and your mileage may vary but I really like it. It's stylish and trendy, but still got a classic touch because it's so thin.
Speed: great. I got an Antutu Score of 17107! For what I do with a cellphone this is more than enough processing power. I do not play any games, so I cannot say anything about the performance there but the apps that I use a lot (Evernote, Flipboard, Memrise, Duolingo, Springpad, ezPDF Reader, Kindle, Aldiko, UB Reader) run fast, snappy and without any lag.
Battery: I got the cellphone for about two weeks now and use it a lot. Under heavy usage (WiFi, GPS, DualSim, a lot of surfing) the battery lasts for about two days. Under normal usage it may last three or four days, maybe even five.
Camera: I'm not a fan of any cellphone cameras, but this is one of the better ones.
Delivery: ok, this is not about the cellphone, but the delivery was very fast!
Really, there are none. Except if you want to root it.
I can live without root access, but if you don't, look on the net for a proper instruction. It may depend on the ROM, but there may be some problems with a process that runs in the background of this phone (wland) and you have to get rid of it if you want to root it.