I very much like Defraggler. It is simple and easy to use on my Windows 10 machine.
However, compared to other similar products available, it lacks in performance overall. In particular movement of files during defrag and performance during analysis.
I would also say that the compaction algorythm needs some tweaking to be more efficient. There should be some addtional options because "Compact" means different things to different people.
I would suggest the following:
1) Defrag and compact for maximum free space. (meaning all files moved to blocks near the start of the partition and free space in one contiguous block.)
2) Defrag only. (do not attemp to compact partition)
3) Only Compact Partition (no defrag)
4) Defrag and Compact placing most used and .exe first.
5) Defrag and Compact placing large files last (similar to what is available now)
6) Defrag and Compact erasing freespace at end of compact (no latent data - understanding this is slower)
Also this application seems to run as a low priority user application. An option to run as a higher priority (especially when scheduled and running unattended) should be available.
Make an Open Source version of other file systems and platforms like Linux and Mac.
