Cloud9 and DigitalOcean hosted VM instances were too small (Cloud9 offers up to 2.5 GB RAM, 1 core; DigitalOcean up to 8GB RAM, 4 core). I now use Cloud9 for its fancy IDE, but only as a SSH workspace. I use Google Compute Engine as my VM instance. I port forward from the VM instance to my Chromebook to run jupyter notebook using the app "Secure Shell" (screenshot attached with options). I used the VM instance to create the id_rsa key pair for my Chromebook.
why chromebook: cheap, cloud-based so easily replaced
I don't use cloud9 for debugging. I use pdb for debugging and pytest for testing. I use the IDE mostly for code navigation, autocomplete, and managing packages with many files
so far avoided needing chrome os's dev mode. using now for 2 months.