I use Defraggler on all my PC's by now, it's just great.
The only feature I really miss is to defrag more than one disk at a time. My computer has several internal HDs and a lot of time also some USB drives. When I see the resources used to defrag one drive, there's room for at least 2 more drives.
Do notice that I want to do separate drives, not partitions. Defragging 2 partitions that are on 1 drive would only lead to a very slow processing speed. But multiple drives should be ok.
Keep up the good work.