Your biggest concerns, maybe:

+ Bandwidth limitations (the $5 instance has 200m/s I think)

+ Lack of additional services you get in other clouds (email sending with AWS SES, for example). It's ok if you just need instances, shared storage, shared IPs, availability zones, backups and an API.

+ Response capacity. I'm not sure if it will be better or worse, but I think it's not the same team, architecture, core infrastructure, etc compared to your current providers... this may require some research to understand if it's a concern for you.

+ The "private" IP of the instances, so you can talk with instances in the same region, is in a shared network with other clients (or at least, it was the last time I did check).

+ Some services (balancers, ipv6) have been released recently, so maybe they are not so "mature" as in other providers. Didn't test any of them here, sorry.

+ Some times, the kernel version in the repos, and the kernel version available for the instance from the API or web interface, are out of sync (at least in Debian instances).

Said that, the instances and the service, perform as expected.

You also have "cloud init" and an API in digital ocean, so you can hook your configuration management system, to automate actions, scaling-up, scaling-down, etc.

They notify for planed maintenance.

As in every cloud provider, sometimes you spin up an instance, and you see lot of old traffic and requests (crawlers, bad dns's, etc). This is no different here.

I think you should make a POC with a pre-production environment... this is cheap. How big is your app?