I've had my mi5 from geekbuying about a week now. It's an amazing phone, I went for the white 64gb from Spain warehouse, took about a week to come. Obviously eu so no import charges.
Now the phone was loaded was an after market (carrier?) Rom, listed as miui 7 stable. As it isn't official it cannot update at all! And you need to be wary about what's on the phone. If you head to the mi forums there are guides to loading official miui roms.
You do however have to unlock the bootloader and this can only be done by Xiaomi. It's an online process and requires them to approve your request. There are guides to this also.. I followed them and it was approved a couple of hours later. I was then able to unlock the bootloader and install miui8 global stable. Which works great, and it's such a cracking phone for the money.
Oh and get the black Nillkin case from the jungle, it's black and clips round the phone perfectly, tho it did have to ship from China.
Any questions just ask.
Mick