While I understand the reason for the popups, they are increasing in frequency to the point of borderline adware behavior.
I have many free products that I have installed, and use. Some are other types of malware scanners, some are utilities, some are games, and even a free firewall. Not a single one of these other programs generates seemingly random popups in this fashion. The ones that use advertising have a very predictable pattern where they display ads when certain portions of their program are used, or opened by the user, or if a specific button is clicked on.
I can understand the reason for the ads, but there has to be limits! Before, I'd only see these Avast! popups once, or twice a day (not counting the previous database update notifications, which I kept disabled) and now I see them what seems like every few hours, and the ones I see for Grime Fighter, are misleading in that they make you think that grime fighter is installed, and ready to run. You click on that to run it, and it takes you to the Avast! store to purchase, or upgrade... Again, this is borderline adware behavior.
I use popup blockers, and ad blockers on my system for a reason. I don't like to see ads and popups in my face on a constant basis.