Using DNS-O-Matic allows you to pick and choose what dynamic DNS services you want to notify, all from one easy-to-use interface.
In your DNS-O-Matic account, for the domain example.com with an A record for dynamic.example.com in your Cloudflare DNS settings, enter:
Username: <CLOUDFLARE ACCOUNT EMAIL>
API Key: <CLOUDFLARE CLIENT API KEY>
Your Cloudflare Client API Key is found in the My Account section, linked from the top right of the Cloudflare dashboard.
One limit: if you have multiple A records for the hostname you are updating, DNS-O-Matic will update the first record found, not others. (For dynamic DNS, multiple A records for a single hostname is unlikely.) One possible workaround would be to change additional records to CNAME records pointing to the original A record.