Disclaimer: I work at Google but I do not work on the product, so this is my personal experience.<p>I recently tried out Cloud Container Builder before it went public. I host a lot of small personal Docker projects on my private GitHub repositories and build Docker images for them using CircleCI and push them to GCR (Google Container Registry). Once you figure out how to do this with $your_favorite_CI_tool, it is easy. However it took me about an hour to build this Circle CI and I had to do some tasks like set up Service Accounts, copy keys around etc.<p>Google Container Builder eliminates this completely, you just connect your GitHub account, pick what you want to build (every commit, branch or tag) and specify the image name you want to build and forget about it forever.<p>It runs faster compared to free CI services I've used in the past (probably because image pulls are fast b/c Google Networking, but I'm not sure how much CPU is allocated for builds). Also if you're pushing to GCR, then it'll be faster to push images as well. So overall pull/build/push cycle is just fast. To compare, build for a very simple image I have (base image docker.io/library/python) takes 3m30s on CircleCI vs 1m10s in Google Cloud Container Builder. That's 3x faster.