thanks, i received the key and it's my opinion.
it's performance is good enough,
but interface isn't much efficient.first of all it doesn't support drag and drop, secondly let's consider you have lot's of files and you open each one to see if you need it or not and decide to erase it; choosing shred with data shredder will open a new window for each file while i expect to add them to a list in single window, checking file permission is an annoying step for most people ,it can't be disabled and dosn't have an auto feature, user must always do this step manually by clicking next button. and the last down side of interface is
it's size, it covers most of my screen which is 1024*768px and really walks on your nerves if are dealling with lots of files.when i choose to shred a file from file context menu, i don't need to see all features of the program (like shred partition), they could at least hide them inside a menu. and finally adding an option to sleep (alongside of shutdown) after finishing job would be useful.