With Malwarebytes Free, after the Premium trial period ends, it is then only a free on-demand scanner with detection & removal of malware / grayware / PUPs; so it will not be running in real-time in the background slowing down the computer, it will only slow things down a bit when you manually do a scan, and yes it can remove malware.
I have been using Malwarebytes Free off and on for years as a free on-demand antimalware scanner, and
Malwarebytes Browser Guard as an extra security layer for protecting my web browser.
Recently I uninstalled them as I often do as I try different security programs from time to time.
I am currently using / testing
Sophos Scan & Clean, which is a free portable on-demand antimalware scanner, that I have set to automatically scan on startup with Windows Task Scheduler.
It is just one layer among several in my free layered security setup.