I've been running the free version of this for a good couple of years.
Never had any problems with it. Yes it has notified me of a problem a couple of times and told me a Site was not safe. As far as I know I've never unwittingly downloaded anything and when I've done a complete scan - it takes its time but I always seem to be clear of any infections.
it updates itself - and tells me that it has done so
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If a thing ain't broke --- DON'T FIX IT
Experienced in making a mess of things

MacBook Pro on OSX 10.11.5 ,Virgin Super Hub , [ sssh - and a PC wired lappy using XP Pro ] all on
Virginmedia 100 meg