Here is also a review from Which magazine saying you should avoid it.
https://computing.which.co.uk/hc/en-gb/articles/213476449-Should-I-download-ScanGuard-
These type of programs work by "scaring" people in to thinking they have loads of problems on their computer.
You install it and run a "free" scan and it highlights all sorts of errors, which of course it will offer to fix if you pay them some money.
Almost all of the errors they find are NOT errors, they will just pluck a number out the air and say you have "57 major errors" or some such thing.
Also note these companies also set up fake "review" web sites where they look like an independent web site that reviews software, and of course they give it a glowing review.
So BE CAREFUL of any glowing reviews for this product you read on the web, it was almost certainly written by the company themselves.