Is the tool itself dangerous or just deleting the files on the nand?
The tool itself
should be sound - the source is available, albert incredibly messy at the moment. Still, it's early and I want to advise people to be careful anyways (also, with the current version not having fixed text wrapping around to the top of the screen, selection can be misleading in folders with lots of entries, so I'd advise against doing anything in folders with more entries than screen space until I can push the next version out).
Deleting files from the NAND without a backup is more what I was referring to as being dangerous, yes. I haven't experienced any issues with the program itself, besides the aforementioned bug. I tested a lot of file copying to and from SD as well as deleting, so all of that should work just fine (if you're copying larger files, though, be prepared to wait a minute or two for it to complete).