The texture generated by the .js exporter is useless. It does not properly take into account rotation or manipulation of the original texture. This makes Cubik completely useless for MCPE and cannot compete with Blockbench.
Here are images of a model with intended UV and texture in Cubik.
Here are images of the model in Blockbench with a segment of the Cubik-generated texture. As you can see it incorrectly generates certain parts of the texture. I am not going to re-create a texture for MCPE so may as well not use Cubik in the first place.
Here are my export settings.