What does Malwarebytes do well? In a world full of bloated, unnecessary antivirus software, Malwarebytes is the only one I'll trust to clean up a machine. Although I don't ever get malware myself (which is easy if you just browse and download safely and use something as simple as Windows Defender), I support users who are less responsible with their internet use, and Malwarebytes is pretty easy to use and even the free option is plenty to clean up an infected machine.
What does Malwarebytes not do well? There's really nothing I have to complain about. Back in the day, Malwarebytes was totally free, and while I have no beef whatsoever with them trying to make money, the pressure to buy Premium is more prominent in the app, but it's also easy to ignore, and the free version does the trick.
What do you wish you had known about Malwarebytes before using? Nothing, really. As mentioned above, it's pretty easy to not need Malwarebytes at all, but if you or a user does, this is the only tool I'll use or recommend to clean up an infected machine.
Have you used a competitor to Malwarebytes? If so, how does it compare? Windows Defender does a good job of prevention and scans, but can't always protect users from themselves, and I have seen Defender miss malware that Malwarebytes was able to quickly identify, quarantine, and eliminate.