I bought one too.. First I rooted it with KingoRoot windows application (there is an .apk version too but less effective after a few times), then I went to SuperSU.apk uninstalling KR from settings (I couldn't install it without first going to the previous root).
Now I am trying to install Magisk, but I can't find a compatible TWRP.img to install it. Did not have success with Flashify or Flashfire
I use Link2SD with a 2 partitions SD (16GB Primary and 16GB Ext2) and I don't have any trouble.