Here are the items I have identified as missing that I wish Xiaomi had included:\
1. USB 3.0 would have been nice but alas the phone only supports USB 2.0 speeds
2. USB MHT (HDMI Video/audio over USB) is listed as a feature on the WCDMA Snapdragon version of the phone but based on what I have read no-one has been able to get it working yet. That being said, I have had pretty good luck with DLNA to my Roku so I am not hurting, others use-cases might make the lack of this functionality thus far a real sore spot.
3. No LTE support - My phone is working just fine on AT&T's inaccurately branded "4G" network - I.E. the phone supports high-speed 3G HSPA+. It does not support LTE however. In testing on the AT&T network in my area I think I have seen the fastest speeds of 5.5 mbps/down and 1 mbps/up in real-world usage though theoretically 42 mbps/down and 21 mbps/up is what the standard allows for. I did some internet searching though and my 5.5 mbps/down and 1 mbps/up is consistent with other AT&T users with AT&T "4G non-LTE" devices. Also, another caveat, if you are buying a Chinese phone that touts 4G LTE support, make sure it supports the bands that your carrier provides. Thus far, when investigating devices from China with LTE support I find that most don't have any band compatibility for 4G in the USA.
4. The plastic casing - The ding on my device and some deformation from use around the SIM-card release hole bother me a bit. I really wish they had gone with metal but I am not going to complain too much at this price.
5. MIUI - Most love it - I like most of it - But I hate the launcher itself - the other system tweaks are actually quite nice. I replaced the launcher with the Google Experience Launcher and the Google Keyboard as well. Much happier.
6. No Play Store out of the box - All google services for that matter are basically non-existent out of the box. I tinkered a lot an my phone now has any and every googe service I want. If you aren't willing to Tinker, buy something in the US for the US.
7. Bloatware - Along the same line as my feeling about MIUI - This is a Chinese phone... it has a bunch of Chinese software pre-installed - once again I cleaned my unit up substantially so I am not complaining but it is worth mentioning.
8. No wireless charging - Yeah, I really wanted this and no, the Mi3 doesn't have it. Of all the items I have mentioned as "negative" this will perhaps be the most sorely missed for me.
I picked up my 16 GB Mi3 WCDMA for a song and a dance (relatively speaking) from a friend directly in China for $240. If you are buying from a vendor expect to play closer to $280 or $290 delivered.
After all of my tinkering and optimizing this phone works pretty much flawlessly - Android never slows down... ever. Everything runs and and it all runs very very fast. It is an experience I have never really had on an android device, especially one out of China. The closest devices in quality and overall polish I have used were the RK3188 powered FNF iFive X2 and the iFive Mini.
So my conclusion...
This phone is perfect for me. However, I wouldn't recommend it to the technologically feint of heart unless you can get a friend to set things up for you. I wrote an article on my other blog here that includes an updates package that takes care of most everything for you: Xiaomi Mi3: Cleaning, Rooting, and Westernizing a Stable Production Rom. Most folks should be able to handle that. An anything less than $300 the device is a steal imho. The processor is only one generation behind but it is beyond every other processor of that generation as already outline in the article and therefore comes close to and in many cases still surpasses current gen chips. Compared with anything from Mediatek at the moment the Snapdragon 800 in the Mi3 is the clear winner every time, even the much vaunted Mediatek octa-core.
I didn't even get too heavily into how amazing the actual physical design of the device is, or how much I actually love the plethora of additional features included in the MIUI flavor of android (I really just didn't like the launcher, keyboard, and messaging app, everything else is kind of amazing and I replaced what I didn't like). Xiaomi has made a killer product from top to bottom and pretty much left no stone un-turned in optimizing the device, including the Android OS, which is very rare for a Chinese company.
The phone does lack a few features which some might find critical. I have enumerated everything I have noticed thus far so make sure you read carefully.
TNT may or may not sell this item. The issue for us is getting stable supply as these units sell like hotcakes and getting them in quantity can be tough. I successfully used both a U.S. Straight Talk and an AT&T SIM card in my unit and both worked just fine including full-speed data. In short, if you are considering this device and you live in the USA, you are thinking in the right direction! If TNT can get these reliably, we will, and we will do our thing to them and sell them as a complete western package!