Yes, cleaning repeated contacts before merging VCF files is the better approach. If you merge first, the same person might appear multiple times in the final vCard file, particularly when exporting contacts from phone, iCloud, Outlook or Android.
After adding all your VCF files and removing duplicates based on matching fields such as name, email address or mobile number, merge your VCF files. A safe option I would suggest here is WholeClear vCard Duplicate Remover, because it can load single or multiple VCF files and filter duplicate contact fields without changing the saved contact details.
Keep one backup copy of your original vCard files before processing. After cleanup, check the output file once, then merge the clean contacts. You can test the demo first to see how it handles your duplicate VCF contacts.
