So it’s best not to combine CDNs for a couple of reasons.
Cache problems. If you’re expecting a page to be cached for 60 seconds, and you have 2 or more CDNs caching it, CDN 1 might cache it for 60 seconds and then pull from the origin (which is CDN 2) which might return a cached reply, causing your cache timeout to add together and be much longer than you expect (causing stale or old pages to be served to visitors).
Configurability. If you change a setting on CDN 1 you’ll need to change it on CDN 2 as well. Plus, CDNs have different feature sets and if both don’t support the exact same feature with a similar implementation you won’t be able to use it at all.
Finally, DDoS prevention. If a user hits Cloudflare’s CDN, which then fetches from the Quic CDN, the Quic CDN might see a lot of requests coming from a similar IP range (depending on if they respect headers) and block it, which you don’t want.
Your best option is to stick with either Cloudflare’s cache which you configure yourself, or Cloudflare’s APO which performs cache optimizations and many other benefits automatically (APO is paid).