I'm trying to find if they offer or plan to offer these features:

1. Caching. CircleCI and Travis cache intermediate build artifacts (e.g., virtualenv in python) to reduce build time.

2. Github pull request integration (red cross on pull requests if the build fails).

3. Chat integration. Sending a message to slack or hipchat when the build fails.

4. SSH into build container. Very handy for rare but difficult to locally reproduce build bugs.

Interesting offer though. We found that we would pay less than 5$ a month for our build needs and they would run concurrently.