Why does custom domain setup require Cloudflare account?

As Cloudflare users ourselves, we think, that their service is exceptional, and it simplifies the setup in at least one significant aspect: by using their service, the domain will automatically get an SSL certificate for free. Cloudflare protects you from attacks, it is unmetered and it is free. It also reduces support effort for us, as we can provide you with the exact steps to follow to set this up.

We do acknowledge, however, that their free plan does not allow adding only subdomains without top-level domains, so if your custom domain needs to be a subdomain (like: short.company.com, not like short.me) you would need to migrate your whole top-level domain to Cloudflare (we advise you to do that regardless, even if do not use our service), purchase their Business plan, or implement some custom workaround (like redirection or proxy). Using a long domain for short links, however, defies the purpose quite a bit, so we advise you to get a separate short domain for short links anyway.

Top level domains (like short.me) can be set up in Cloudflare for free. They also provide domain renewal service at wholesale prices without any markup, so you will probably save money by transfering your domain to Cloudflare: https://www.cloudflare.com/products/registrar/

We plan to provide the possibility to use regular CNAME setup for custom domains in the future. We are a small startup, and the way our service is made does not allow us to implement CNAME setup cheaply, so we need to get more clients to afford this. Had we not put redirection speed as the first priority of how our service should work, we wouldn't have had this limitation.