Malwarebytes - Friend or Foe?

A client said his computer was running slow. In fact, it was slower than slow. So a Malware scan, check of background programs and a hard drive defrag proved inconclusive. Then I remembered an article about Malwarebytes. The author said that Malwarebytes, for reasons unknown, could start the usse all the cpu's resources. I checked the startup list and the Malwarebytes services. It was only configured for manual launching; however, as an experiment, I uninstalled Malwarebytes