These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Rainbow Factory
Adaptation Displacement: An increasing number of people know about this fic through the Rainbow Dash Presents parody, to the point of accusing Aurora Dawn of ripping FimFlamFilosophy off. FimFlamFilosophy is trying to rectify this by crediting Aurora Dawn every time his characters are used in other videos and linking to the original fic on his blog.
Canon Defilement: Big time. What Cupcakes does to Pinkie Pie, Sweet Apple Massacre does to Big Macintosh, and Cheerilee's Garden does to Cheerilee, Rainbow Factory does to Rainbow Dash.
Complete Monster: Rainbow Dash oversees the murder of ponies every day, but what firmly rockets her into this territory is how she's implied to murder Scootaloo, the closest pony she had to a little sister, in cold blood. It's explicitly stated that Scootaloo's failure at the flight test, sealing her fate, kills the last kind feelings Rainbow Dash had and irreversibly turns her into a merciless monster.
In the Rainbow Factory, where your fears and horrors come true....
Easily Forgiven: Apparently, the whole factory and all the workers within it. All it takes is a public apology for the brutal slaughtering of hundreds of youths and the Princess will let you off scot-free to continue running the place as long as you promise not to kill anypony else.
Fridge Horror: The only reason Fluttershy was alive to become the Element of Kindness was because a worker voluntarily sacrificed himself to become spectra in her place. Imagine if he hadn't.
Even that spoiler gave some info about the exam: The flashback stories of The Cutie Mark Chronicles happened two days after Fluttershy's flight exam. That young.
Which means ponies that don't have cutie marks could have failed the flight exam. Imagine knowing your about to die without finding your special talent...or worse, realizing that your special talent is becoming spectra. (Though, what WOULD that cutie mark look like?)
Score another for Hilarious in Hindsight. The song, by virtue of not elaborating on the exact nature of for-mentioned 'fears and horrors', is quite compatible with the 2013 horror movie The Purge. To an extent, the fic is comparable for the shared plot-devices that the main targets of the murders are the less desirable parts of the respective societies (the poor in The Purge, the weak in RF) and that it has at least been suggested that they harvest the bodies from The Purge for power or some such thing.
Many businesses in real life use Rainbow Factory as their name, most notably, a sandal store in San Clemente, California. Have the song and fanfic boosted its popularity?
Narm: Considering that the basic premise is essentially "Soylent Greenis PONIES!", it's liable to cause a few snorts if you refuse to take it seriously.
Rainbow Dash's bouts of severely Out of Character behavior, ranging from cocking her head back and bellowing out an Evil Laugh, to her boasts of how powerful she is.
Every single adult pony they meet being EXTREMELY cruel to our three heroes.
Visual Effects of Awesome: The animation of both PMVs is extremely impressive, particularly the "Cloudsdale Weather Corp" screen at the beginning of the "Awoken" PMV and the slow-motion shot where H8_Seed bucks Brony Dance Party off the ledge.
We Hardly Knew Ye: Both Aurora and Orion are given little to no development as characters before they're killed off.