First, I sincerely doubt that Microsoft sent you an advert regarding a free antivirus program since they already have one installed on their latest operating systems.

Next, based on only one review I found, TotalAv wasn't rated well by PCMag for it's ability to detect malware. See the link below:

And next, if you already have a paid version of Norton on your computer, it's not recommended to use two different AV products running at the same time. They frequently conflict when trying to detect and remove malware PLUS they usually bog down the computer severely

Hope this helps.