I use FTM2012 (and v16 before that) and have successfully used the built in function to find and merge duplicate people. If you merge from other sources, and as your tree grows large, it is unavoidable to have some duplicates. The presented list of duplicates is never perfect but the ones that are true matches helps a lot in cleaning things up. Only merge the matches you are sure are correct and leave the rest for later or manual. The real matches are usually in the top of list with high ratings. Any way I find it helpful if used with discretion.