My kiasee-ism and kiasu-ism have brought me to verify with XM themselves and yes, my unit bought from SLS is authentic. (huge sigh of relief)
I wish those who are going to compete with many others later at 12pm good luck (including myself).
Let me give a short review after 1.5 days of usage.
1) 5.5' screen: It is very crisp, but of course don't expect retina display or super high def display. It is considered very good for a 1280x720 screen. Pre-existing photos in my SD card are very clear (but could be due to camera quality too). Though it is less than based on calculation, antutu states that it has a dpi of 320.
2) Battery life: Good, better than the S3 which I broke. I bought it on Sun evening, charged it overnight and unplugged at Monday 6am. Plugged into laptop usb at about 0830 am, but decided to take it off after 30 mins to test the batt life. Played with it most of the day, facebook, whatsapp, games, used GPS at night (about 30 minutes in total), lasted to 1% at about 11pm. For today, it was unplugged from charger at 6am, left with 77% as of now (11am)
3) Performance: Not sluggish. Apps launch quickly, swipe between pages is smooth, games are performing well too.
4) MIUI: Simple, easy to use and soothing to the eyes. It is a combination of Android and iOS as it has the flexibility of android, and minimalism of iOS. It looks like iOS (no app drawer) but it can have widgets. Swiping animation between pages can be changed. Many themes of the UI to choose from. Deleting of apps is just tap & hold, drag up to delete (unlike the stock S3 UI, which luckily I installed Nova launcher to replace).
5) Camera: Stock one isn't perfect as it cannot save the photos to SD card. Quality isn't the best too. I installed Lenovo Super Camera and it is awesome now.
6) No 4G: It is probably the biggest flaw I can think of for this phone. But 3.5G is decent for me as my last phone was a S3.
For a $199 phone, it is almost unbeatable. A great replacement phone if you are holding out for the next big thing or waiting for contract to end.