This is exactly what my team told me when they switched from Concourse CI to CircleCI. I was surprised, this wasn't really discussed, but the pressure on the team to deliver features was increasing, and they were struggling to much with all the tooling instead of delivering functionality. So they deciced to switch to something not so sexy but dependable and stable. Funny thing, about 1 year later we got acquired by CircleCI :)

I like to compare CircleCI to a Volvo, not the most sexy thing in the world, but when you need something dependable that gets the job done and helps you to focus on what really matters, getting from A to B, it's one of the bettter choices.

(disclaimer, i'm still with CircleCI)

I looked at their docs. Their "Debug with SSH" feature is something I would have liked to have had many times in the past: instead of adding a CI command to cat a log file to the terminal, then examining it with GitHub's inadequate log viewer (which seems to bug out, at least under Firefox, when logs are too long), I could have SSH'ed in and examined the log files with my familiar tools.

If I may ask, what about CircleCI have you found particularly nice? What tools does it give you that you would miss if you had to move to a different CI platform?