As a matter of fact, phones available for a particular market are designed from the software point of view accordingly. It may not be a good idea to buy a phone which is not meant for India.
In case of you are confident of any tweaks for unlocking the phone from region specification, you may consider buying from those sites.
The phone may or may not support the Indian bands. Please confirm whether the phone can use Indian SIM cards.
Other than the functionality issues, you may also face issues related to after sales service.
The device being from another country, you may not get warranty for the device.
Sadly enough, the Xiaomi Mi 4C is not likely to be launched in India.