Is it safe to use the duplicate files option and erase them
'Safe' in what regard?
What kind of files?
If you are talking about System Files then NO it is not safe to delete them. (Unless you know exactly what you are doing and are doing it for a particular reason)
The duplicates of certain System Files are needed to make sure that your computer functions properly - so leave them alone - if you remove the System File duplicates your computer may (will) stop working properly.
Better still, exclude System Files from your duplicate searches altogether by ticking the 'Ignore' box for them.
(It should be ticked by default, but people do untick it).
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As for your own files, photos, video, music, documents, etc. It can find any duplicates that you may have for you, but only you can decide which you want to keep or not.
What it finds as being a duplicate depends on what you have set it to look for in 'Match by'.
So for example if you only ticked the box for 'Name' it would find any and all images named 'Photo-01,jpg' as being duplicates.
Of course the actual images themselves may be totally different, but you only told it to look for files with the same name.
Note that 'Photo-01.jpg' and 'Photo-01(copy).jpg' would not be found as duplicates by that name-only search, because the names are different.
I find that Match by 'Size' and 'Content' as show above are the best to tick to quickly find any files that are exactly the same, no matter what they are named.
(You could just tick Content to find the exact duplicates, but I find that ticking Size as well makes the search quicker).