Ignore that 1 star reviewer. It sounds like it was written by a bot. This is one of the best riffs they've done. It was basically hilarious lines from beginning to end.
As to the points in the 1 star review: the guys never made fun of Whizzo's stutter, just his silly act. I don't recall any mentions of racism, and if there were any they were likely tongue in cheek, and they never made fun of any of the children. The most they said about any of them was pointing out a little girl's loud coughing, which was very pronounced when it happened throughout the film. It was impossible to not notice it.
Overall, this is one of the best ones yet. The intro where they set up the movie as "one clown's descent into madness" was also perfect for the film. If you find this on YouTube it's also got a great short before it, which involves a few sentient Christmas trees. Also bizarre and hilarious.