MalwareBytes is a great and respected anti-malware product. The registered version is preferred as it offers real-time protection which is of paramount importance.
Even if you already have real-time protection and scanning through another security product, MalwareBytes free version can also be great alternate scanner.
Having multiple scanners installed can help with malware protection as some scanners may pick up malware that others don't.
Whilst having multiple products offering real-time protection should be done cautiously, having multiple (manual) scanners would be a good practice.