It makes me instantly skeptical :)
My notes here: http://anil.recoil.org/2014/03/26/codio-now-has-opam-support...
Another reason is that Nitrous.IO has a desktop client that uses unison to keep files in sync. This means I develop locally using my favourite IDE and I get to preview it instantly on my nitrous.io box, I say instantly but I'm sure there is some latency, but I'm lucky enough to have an internet connection where CTRL-S, ALT-TAB, CTRL-F5 results in my newest code being ready without having to wait.
Sorry but I was hopeful that Codio could live up to it's claim, but the fact I can't even run their default PHP file is pretty sad.
Check out the docs on using PHP in Codio https://codio.com/s/docs/specifics/php/, but it's a simple matter of `parts install php5 php5-apache2 && parts start apache`, and you're up and running.