Aspect's Workflows product works with your existing CI system. Many organizations have made a commitment to building on a particular platform, like GitLab CI, Amazon CloudBuild, CircleCI, Jenkins, and many others. They have tight coupling with it, in that developers have written configurations and cron-style scripts specific to that CI system, and these are generally undocumented and untested, so it's a risky move to switch. Furthermore, in some companies the team that "owns" the CI system is separate from the developer infra team who might deploy Bazel, so there's an organization impedance to get the needed decision-makers to agree.
However, Aspect clients often ask which is the best for Bazel, and that answer is quite clear to us: it's Buildkite.
Custom UI: Annotations
Buildkite has a feature which allows a build tool to produce Markdown which is rendered as a separate block in the results UI. You can see some examples in this Buildkite blog post
Aspect CLI has a plugin which translates Bazel's build event protocol directly into Buildkite annotations. This means that developers don't need to click away from the CI page to some "Bazel results" UI. They get exactly the feedback they want, in the same place that every other build tool shows it: one click away from their PR by following the red "status icon" link.
You can see some examples of Aspect CLI annotations on the documentation site
Connection between Bazel and Buildkite
There have been Buildkite talks at Bazel confererences and Bazel talks at Buildkite conferences (Unblock) The core Bazel team uses Buildkite for the CI of the open-source project, and the rules ecosystem.
This one is hard to quantify. Our experience working behind the scenes with different CI systems is that Buildkite is substantially better engineered. This comes across in the polish of their UI, the thoughtfulness of the API, and the communication style of their documentation. We've been working with them since being on the Angular team in 2017 and have had only positive experiences with their product and service.
Discounted pricing is available for Buildkite plus Aspect Workflows, thanks to our Channel Partnership with Buildkite. If your company would rather not deal with procurement to two different vendors, we can also manage these together under a single contract and single point-of-contact. Please email us at firstname.lastname@example.org to take advantage of our Buildkite partnership.