One reason for them to scale to 10x F-Large on Heroku is that their app gets super-slammed (150x more than average traffic) around college application deadlines

One reason for them to scale to 10x F-Large on Heroku is that their app gets super-slammed (150x more than average traffic) around college application deadlines. So they can spend most their time on cheap Heroku and just temporarily scale to super expensive Heroku for a short time.