UFW is a host-based tool, while Digital Ocean’s Cloud Firewall is a network-based one. Using DO’s tool will not only provide reusability of rules (deploy inbound / outbound rules to many droplets - or even tags - at once) but also processes them before even getting to the droplet. Don’t get me wrong, UFW is an amazing, full-feature and extremely efficient tool, however when it comes to deploying shared common rules to lots of servers, it’s a bit time-consuming and repetitive task.
When you only have a single Droplet, using UFW will be more beneficial as there is no need for scalability. Additionally, when you need to use custom defensive mechanisms like Fail2ban, enabling UFW really helps too.
Hope this helps!