Malwarebytes Anti-Malware now forces you into taking the free trial whenever you download it for the first time or update it later on. I've found that the 'run in the background' method of working that the full (Pro) version uses can noticeably slow down my computers.
For that reason I've ceased recommending MBAM as a free anti-malware solution. My preferred option is now AdwCleaner which, since it's now owned by Malwarebytes anyway, is just as good (and with no 'free trial' to worry about):
https://www.malwarebytes.com/adwcleaner/
However you don't need to ditch MBAM. You can simply disable the free trial if you want to:
https://support.malwarebytes.com/docs/DOC-1033
(Note that MBAM automatically reverts to the free version after 14 days anyway if you don't buy the Pro version).