Cloudflare doesn't offer trials at the moment. If you want some blanket advice, there's a few cases where APO can't help in:
If your WP site is super static and you can simply just force caching of everything, will always be faster then APO
If your WP site is super dynamic and you want constant updating, OR if most of your users stay logged in, both will bypass APO handles the magic of updating site clearing cache seamlessly and being a magical cache layer that just works.
If you could make your site super static/force caching and just manually clear, you'd have better performance then w/ apo, for example