Why are you on CloudFlare in the first place? It allows many features and they are excellent:
DNS management.
If there are many accounts, it can increase many benefits.
When I tested Cache, I understand Cache Rules should be placed inside CloudFlare system if you like to work all cache benefits. But testing NGINX, it has also benefits. So, I try to secure IP and CNAME but control my cache rules.
Ok from what I understand free plan can lower website speed sometimes when CloudFlare is really busy because it prioritizes traffic from paid customers. Just so you know.