Hello. A tiny suggestion, why not calling "Fill gaps" to "Defrag freespace"?. I think it's clearer and easier to understand. Also, that option still creates further fragmentation (Defrag freespace). Using version 2.07.346
A better term should be "align files", "compact files" or "defrag contiguous freespace" I think "fill gap" could be just as confusing to some people.
As for defrag freespace (both options) I've also noticed it increases fragmentation even though the drive was previously 100% defragged.
Richard S.