The main thing I love about semaphore is that it's easy enough for beginners of code quality but also has advanced features that are very useful when you're dealing with large scale applications or have complex build pipelines.
It doesn't allow me to see how many tests get run in my pipeline before they fail so this could be an issue if using it in conjunction with Jenkins. If you want something free from cost then use Jenkins because Semaphore will charge your credit card after 30 days! I'm currently working at a startup trying to improve internal software testing infrastructure.