Pardon, but I know all this, how to root etc ZTE 1.0 resp. 1.2 - and I have a rooted ZTE 1.2. The problem is, that after installing 1.4 you have no root, you can't get the su-binaries in /system/xbin.
ZTE Open / roamer2 (B2G 1.2. / 1.4 -prereleases)
Galaxy Tab 3, 7'' (SM-T210)