Note that its the Mediatek chipset and not the Snapdragon version. So I bet it will have a custom China or Dev ROM and you most probably will have to unlock to flash Global ROM. Gearbest don't add bloat on the custom ROMs so its not a must but you will most likely not be able to OTA upgrade unless you flash.
Gearbest support I would say is a hit & miss. I have had no problems with them when I had a phone with reboot-loop that I send back for replacement. Some people here had issues with them. Xiaomi also do have local support agents now, so you might try your luck and have them cover warranty related repairs if you have them.
Other things to note: Helio X20 score higher on bench than SD625 but is more power hungry and also lack some custom ROM support. So it all depends what your needs are. Both the Helio X20 and SD625 versions of the Note 4 are better than the Note 3 so both would be upgrades.
Edit: also note the Note 4's Helio x20 use Mali T880 which doesn't perform as good as the SD625's Adreno 506.
Personally I would recommend
http://www.gearbest.com/cell-phones/pp_613145.html instead of
http://www.gearbest.com/cell-phones/pp_620670.html if you go via Gearbest.
Edit 2: Interesting read re Note 3's SD650 vs Note4's SD625 -->
http://in.pcmag.com/xiaomi/111758/f...apdragon-625-is-the-right-choice-for-the-xiao