The main point of this article is to use a Cloudflare cache-everything rule and use that caching to create a free image host. From the article:
> I'd heavily recommend adding a page-rule to set the "cache level" to "everything", and "edge cache TTL" to a higher value like 7 days if your files aren't often changing.
The word on the street is that they will start throttling and contacting you once you hit several hundred TB per month. 
Of course this is still extremely generous and the upgrade plans are usually still several orders of magnitude cheaper than any cloud provider per gb. But don't build a business or hobby project around cf providing unlimited free bandwidth forever.
(basically search HN for cloudflare + non-html)
Should CloudFlare later ban you for the practice, will the random support person you reach unpack the CEO's comments here and ensure nothing changed internally that prevents allowing your continued use and advocate restoring your account for you?
If the perk saves you money, you put that money in savings. Once your budget expands to depend on that perk you are trapped, and when it goes away the pain will be noteworthy.
In words that are more applicable to a business case: You have to have a strategy for when the Too Good To Be True situation ends, because it will, and you have less control over when than you think you do.