Ultracopier is free and open source software licensed under GPL3 that acts as a replacement for files copy dialogs. Main features include: play/pause, speed limitation, on-error resume, error/collision management ...
Supercopier have been merged into Ultracopier (it's just skin).
The project is mature and oriented multi-platform and data security.
On lot of condition your can improve the performance very the settings: inode thread: 16.

Is actually more of 1 millions of users and more than 5000 linux users each days. The project need funds, improvement in Qt (not only get but to set the file time, and QFile flags to say the linear access is the 2 biggest problem with Qt), but before all interest to the distribution to have updated package and file manager interest to have native usage (asked since many years).
Useful link:
Comparison of ultracopier, SuperCopier, TeraCopy and copyhandler
Speed/Security of ultracopier, SuperCopier, TeraCopy and copyhandler
Article on this can be very useful to do progress this project into the open source (KDE/Gnome/Qt dev will see it).