I think they just don't want you to serve large stuff, because their CDN isn't optimized for that.

I serve all kinds of files <10mb via CF, that includes audio, video, images etc.

Files over >10mb I handle myself. Around 100TB is handled by CF each month and around 700TB by my own servers (4 Hetzner dedicated servers).

The whole setup costs me around 300 euros/month paid to Hetzner, and 20 to CF. That means I pay around 40 cents / TB.

So far CF hasn't complained, and I've been using them for years. Though they try to pitch me their higher priced plans now and then.