They're not actually giving away service that others charge thousands of dollars a month for, for free. If they were, most of those others would be out of business. Their free and self-serve tiers are nice and can even be good deals (you really get a lot out of that top-tier self-serve plan, for the money—watch out, some of the lower ones didn't have any SLA at all, last I checked) but if you're pushing serious bits, you're gonna end up pushed to a thousands-a-month enterprise plan.
TL;DR unless you've got an enterprise plan with them, yeah, "use it and hope for the best, 'till you get a notification from CloudFlare" is pretty much how their plans work.