The Censor effect was broken in FCPX 10.4.9. The broken effect cannot be keyframed to animate.
Censor SC fixes that. It is not an exact replacement but offers all the same functionality.
Differences in parameters:
Most of these parameters are similar enough to the original. However, the Amount simply fades the opacity of the effect layer.
There is no Effect Boost in this, but you can click and drag upward on the Pixellate Scale and Blur Amounts to intensify them.
The Mix parameters fade out the effects (Pixellate and Blur).
Darken can “grade” the darkening that is only a menu selection in the original.
Curvature allows you to change the shape from a circle to a rectangle, again, which is only a menu selection in the original.
Radius and Aspect work pretty much the same as the original Censor effect.