This is actually a pretty cool app IMHO. Lot of cleaners focus on things like history stored in the registry, which *to me* is kinda meh. Installing KCleaner 3.6.6 adds one registry key for uninstall, plus one key for KC Softwares -- you get the program's folder, plus a folder under C:\Users\ [UserName]\ AppData\ Roaming. Copy the program's folder, "KCleaner", to a copy of Windows where it hasn't been installed, run it, register using the GOTD data, and it's now portable. All the settings are now stored in a settings.ini file.
You register the app via the "?" menu -> About. Works fine but it could be made clearer that that's where the dialog is. If you select Expert mode, & you probably should, then click Simulate, it shows you what it plans on deleting, with a checkbox for every item. The list includes the path to each file, which can be pretty long, and the window adjusts the column width to fit. That means that you have to keep scrolling side to side to see the size of each file, and whether it's worth the effort. Drag the window border to resize it -- as soon as you do the file path column becomes truncated, so you see the file name & its size at the same time.
Why I think it's a winner... I have a copy of Win10 that has [for years actually] shown an erroneous 3+ GB stored in the Internet Explorer cookie/cache files. The error didn't mean anything, having no effect at all, other than twice a month when I updated that copy of Win10, I'd run Dusk Cleanup, see that 3+ GB, and it would bug me. Every once in a while I'd try a cleaning app to no avail. After running KCleaner I checked Disk Cleanup, the 3+ GB was still there, but this time disk Cleanup got rid of it. YEAH!