Hey Dave Hansen-Lange the UI performance is as pleasing as Google Drive in overall. I have no better way to describe my experience at the moment.
You can share file editing, terminal session and overall environment state — really pleasing for remote pair programming. There is no lag in typing, as long as you have acceptable internet connection. Meaning, the guys at C9 have done excellent job at providing IDE in the browser, but you can decide to use the desktop version if you have high requirements on this.
“reload the app”: makes me think you expect “hot reloading”? That’s a technology-specific thing which is up to you to implement, usually node.js related approach which is generic to the editor. Auto-save? is a setting ;)
Collaborating is my favorite feature. I do that almost every weekend. That is also how I heart about the tool in a coding competition. The winners took advantage exactly of the real-time collaboration features.
I’d encourage you to experiment as much as you can. I personally do that to evaluate what are the edge cases I can handle.