I've used the conventional U-shaped fret files and I do have a couple of them, but I still prefer a good well prepped triangular file or my Gurian quarter-round file. They are what I started out with and they just feel like the right tool for the job to me. The goal is to remove as little material as possible while maintaining that leveled surface at the peak that you just spent time developing. I like working from the side and being able to clearly see exactly what I'm doing . .