polyfix vs drywall compund vs other

We are attempting to skim coat over a stomp textured ceiling (400 square feet). Scraping is not an option. Pics of ceiling available at: http://www.math.uwaterloo.ca/~mrubinst/ceiling/index.html
We're not sure what material to use. The lady at home depot suggested we use 'Polyfix smooth surface filler'.
Is this a good choice? Besides being expensive, it seems to me that it would be better suited for fixing small imperfections as opposed to smoothing out an entire ceiling. Would it be better to use drywall compound? What about some sort of plaster?
Also, any good tips for skim coating a ceiling? I want nice results and want to avoid having the stuff crack, fall off, etc.
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