Mac is running slow and freezing after downloading MacOs High Sierra ?

From my past personal experience, I believe that the facility is safe to use!

I acted as a 'guinea-pig' for the developer some years ago!

You can see an example of such a report if you look at the post I made here:-

Re: Why does my typed text 'jump up' to the line above where I'm typing?

HTH

D.

What year is your mac?

A few months ago I encountered some issues with the GPU after upgrading to 10.13 I updated my NVIDIA driver, and it immediately improved things.

Some more info about what you're doing when the mac is slowing down

let me know

Please install EtreCheck and post the report.

http://etrecheck.com/

It shows diagnostic information about a Mac and what software is installed that may cause problems. No Personal info.