I downloaded the demo and the first thing I noticed was the UI is very confusing and not very clear about what was happening.
You are greeted with a very small UI window to drop you files into, but offered no immediate options. Only by clicking on the 'Preferences' button do you get to make any selections that will effect the naming of your files. This presents the first issue: a slide down window that obscures your file list, and tabs within that window for yet more options. Not very elegant. File Naming and Saving Options are in separate tabs. Is that really necessary?
And then, ANOTHER tab at the bottom that open ANOTHER slide out widow for Preset Lists. The interface is like a game of Jenga. Pull this out of here, and this out of here, and if I click here, something pushes out over there.
Other file renamers like ABFR9 and Renamer present all of your options in one pane allowing you to see immediate feedback in your file list. The commands available are limited to one at a time. So if I want to add a Prefix and a sequential number, that requires two passes.
And you still don't see what is going to happen to your actual file names until you hit the Rename button. Luckily there is an Undo button if things go totally bonkers, and trust me - they will.
If it takes longer to figure out the interface than it does to rename manually, with uncertain results, this qualifies as a "Delete App Immediately" .
Pros: It does rename files
Cons: Confusing, multi pane interface
No WYSIWYG feedback