IIRC Cloudflare is the only registrar that doesn’t mark up from wholesale prices, or something like that. Basically makes them cheaper than most other registrars. I think the point is that they can then sell you their other (related) services more easily — the services that actually make them money.
Reading through their mail merge tutorial, their method looks insanely risky: putting all addresses in “to” and rembering to click another button.