Avast has good detection, but for my feelings, has also many not usefull parts in IS. Yes, is posible unclick instalallation, but still feel as Emsisoft is far more clear and has things, what I personaly need to have only.
I remember last year, there was an identical promo of Avast IS one year free.
If I remember correctly, I got the license, but by uninstalling and reinstalling it after a bit of time and entering the same key, I was not able to reactivate the product.
Now I've not yet tried this new promo, but my advice is to keep Avast IS for the duration of the license.