We pay for CircleCI at $WORK and it’s pretty good. You get up to 40x concurrency in the “Pro” plans and I’m sure you could work whatever you need into enterprise.
My biggest complaint has been it lacks an very useful built in ability that Travis had, which is automatically running your builds on the merge of your current branch and target branch. You can right a script to do it yourself, but there missing some environmental variables to do it easily (because the build can start before the target branch is known).
I can echo all of this - we also pay, we're very happy, the concurrency is nice (I believe they're bumping it to 80x soon - when my coworker asked "but what's the catch" I realised we pay by the CPU minute anyway so higher concurrency is a win for CircleCI -and- for US ;) ).
I've also hacked about the 'merge' problem but it's not entirely satisfying.
That all said, with GH actions currently being entirely free, and doing PRs better than CircleCI, we might shift our focus there.
My biggest complaint has been it lacks an very useful built in ability that Travis had, which is automatically running your builds on the merge of your current branch and target branch. You can right a script to do it yourself, but there missing some environmental variables to do it easily (because the build can start before the target branch is known).