Just triggered a Ransomware Shield warning under the default Smart Mode - for a 2013 version of FFMPEG.EXE - so it appears the Smart Mode (Ransomware Shield) is working in Avast Free. And it allows you to permanently whitelist the detected program from the warning popup - which is nice.
I have to assume the internal "Trusted Apps" list is either very large (and includes obscure 20 year old Hex Editors) or it is using some other specific criteria to classify an app as "UnTrusted". I will leave the Ransomware Shield running for now and see if it gives me any problems - it will be a nice additional layer of security if it plays well with everything else on the computer.