Avast, unlike Piriform is a large, already established corporate entity. Piriform did exactly what they wanted to do, develop a decent piece of software and then sell the rights off. The direction Avast is taking sounds much like another company that offers free applications and asks if you want to install antivirus ware with it; Adobe. It's a common strategy.
Once my paid license is over, if I find the software doesn't perform any better, I'll just move on. There's no shortage of software manufacturer's out there.
Here's a tech-radar article outlining a few that sound just as good, if not better. The article is a year old, but in doing a quick scan of reviews, most mentioned here get decent ratings.https://www.techradar.com/news/the-best-free-alternatives-to-ccleaner