You’re locked into using their DNS servers. Some people are okay with that, but I don’t like arbitrary restrictions on my domains nor how much control Cloudflare have over the internet. Cloudflare’s domains are a loss leader - they sell them at wholesale price and make $0 profit - with the idea that you’ll get hooked on their other services and become a paying customer. Trying to ensure you use their services is the main goal, which is why they lock you into their DNS.

I prefer Porkbun - they’re a bit more expensive (still cheaper than Namecheap though) but you have full control over the domain.

In general, you never want to have both your domain and your hosting or CDN with the same company, as they can hold your domain hostage if there’s any ever concerns with the site.