I loved it-- I loved having separate environments per-project. I enjoyed the collaborative features as well (send a link to look at code or preview something, etc). I see a lot of potential with them and I would love for them to be more mainstream.
After Amazon acquired the company I cancelled my subscription (I was paying annually.. I think it was $190??). I knew Amazon was going to murder the service, require an AWS login and who knows what.
I have tried others since then like code spaces and some open source/self hostable solutions (I have even tried the old self-hostable Cloud9 code).
Ultimately, I gave up on it... why? I didn't like the idea of self hosting (more attack surface area, etc). I didn't like any companies offering the service.
I bet it's hella outdated and full of security issues now though.