Well I Myself Been Using Avast Free From like 2006 days, I still believe it provides the best protection of any free product around, doesn't affect system performance, System Images are done monthly for household systems as it's good to do to keep the machines backed up in case any disaster happens--whether it's hardware disaster, software disaster or god forbid Ransomware disaster accidently
Can't predict what will go wrong, Avast provides the best protection its able to, also depends on how safe and cautious users are using there computer systems, person behind the keyboard also responsible for there own system security, maintenance, and updating of programs (including 3rd party programs)
I haven't had a serious infection since late 2005 before I switched to Avast with new system
Learned the following lessons since
Backup Backup Backup, keep at least 2 copies if possible, one local and one off site in cloud storage
practice safe surfing
update all programs regularly
so far so good myself in terms of any infections or anything