True, but I found that they could have a hard time defragging a large file, if you are close to the capacity limit.
I even had problems getting them to defrag a big iso, that there were lots of "uninterrupted" free space for.
If defragging fails, then try my suggestion.
After my attempt to defrag failed, I formated my drive and started to transfer the biggest files first, one at a time and checked that they were not fragmented after each transfer.