alt Hacker NewsGithub being a single pane of glass for developers with a single login is pretty powerful. Github hosting the runners is also pretty useful, ask anyone who has had to actually manage/scale them what their opinion is about Jenkins is. Being a "Jenkins Farmer" is a thankless job that means a lot of on-call work to fix the build system in the middle of the night at 2am on a Sunday. Paying a small monthly fee is absolutely worth it to rescue the morale of your infra/platform/devops/sre team.
Nothing kills morale faster than wrenching on the unreliable piece of infrastructure everyone hates. Every time I see an alert in slack github is having issues with actions (again) all I think is, "I'm glad that isn't me" and go about my day
I run Jenkins (have done so at multiple jobs) and it's totally fine. Jenkins, like other super customizable systems, is as reliable or crappy as you make it. It's decent out of the box, but if you load it down with a billion plugins and whatnot then yeah it's going to be a nightmare to maintain. It all comes down to whether you've done a good job setting it up, IMO.