If I'm already using Cloudflare for website security, do I need to also use 1.1.1.1 on my devices?

Using Cloudflare for website security protects your website from attacks. Using 1.1.1.1 on your devices protects *you* from malicious websites and improves your overall DNS privacy and speed. They serve different purposes and are complementary. It's generally recommended to use both for comprehensive security and performance.