But this makes no sense. Trial versions are made for people to test commercial software, and then buy if satisfied. Why should I test free version if it's far from similar to the paid one? How can I decide to buy the paid version after using the free version? Do you think that a nagging screen can make me buy it? It only can start a threads like this one.
The protection offered by the free version is the same as the paid other than a few extra added features.
It's obvious the ad for "paid" placed in the free version must bring in revenue as avast would have the details on where customers are purchasing through, if it didn't work then it wouldn't be there would it.
Like I said you don't have to look at the UI ad, what's the point in sitting there staring at the UI - you open the UI and do what you have to do ( adjust settings, check virus chest, etc ) then close it, if the ad placed in the UI bothers you that much you are quite welcome to use something else but don't expect people to condone the use of pirated avast licenses simply because you don't like an ad.