Ishi,
Most plugins are multi-threading - they handle different parts of the image simultaneously. This accounts for their speed. This usually limits the algorithm to being a filter.
This plugin is single-threading because it has to pre-process the image as a whole repeatedly before applying the math. all parts of the image are processed multiple times sequentially.
Unlike most edge faders that blur the alpha channel this one actually fades from the edge of the transparency inwards by mapping the edges then creating a receding effect allowing 256 levels of fade and complex non-continuous masks.Those were the requirements I used developing the plugin and those requirements would not be met using multi-threaded code. I at least, could not find a way or I would have wrote it that way.
Hope this makes sense.