MacKeeper

You may find this helpful:

Do not install MacKeeper - Apple Community

The rule is to never install apps that are:

• Cleaners
• Optimizers
• VPN
• AntiVirus

Simply following that rule will tell you not to use MacKeeper. If you do use this piece of software we are here to help you with any issues you encounter. The first suggestion will always be to remove MacKeeper.

No, it's not trustworthy. In fact, it's pretty close to being malware itself.

Your Mac doesn't need third-party software to keep it running efficiently. Anything you add that claims to do that will just slow it down and gum up the works.

See this article, which includes a section on such software:

Effective defenses against malware and ot… - Apple Community

No it is not. Do not install or uninstall and tell him to ask MacKeeper for a refund.