I couldn't add a SSH key. It seems this was because of a bug in the JS library 1.7.3 that the control panel uses. So I tried to disable JS: the control panel cannot work without it. I don"t care about dialog boxes sliding from the top of the page, I just want a rock-solid interface that works on any browser. HTML is there for that, but DO prefers a flashy control panel.
I was just experimenting before deciding to migrate professional and hobby projects to DO. Now I have my answer. Maybe the back-end is good, but is the front-end is that bad, it will be a pain and a security concern (cf Linode and their front-end failure).