My issue with the Cloudflare registrar is that if you are using Cloudflare for DNS too, you’ve basically given them control over your domain. Yes, they don’t need the DNS part to redirect your domain to a different address, but you’re putting more eggs in the same basket. If you also use their hosting (pages or workers), you’ve given them full control over the entire project. I prefer to use the latter options, without using their registrar, just in case there is a problem or misunderstanding with a site, I still have the authority over DNS in a different provider and can switch quickly.
The registrar has control over your domain regardless of where you host DNS, since they could change your nameservers if they felt like it (or perhaps by accident). True I doubt a company like Cloudflare would do this (there would be huge repercussions), but it's nonetheless true that your registrar does hold all your eggs no matter what other decisions you make.
