Vic, even with system setting for allow long path, seems individual programs choke. Individual programs themselves have to allow for long paths. If they do, and Windows setting is set to allow, then no problem.
An increasing number of programs are allowing/handling long path length. One example that I often use is TreeSize. TreeSize, more meant for other uses, at least shows directories and files exceeding 256 characters in length in red, thus allowing one to rename to shorter path, from within TreeSize. Upon 'refresh' of the folder, the now-shortened path will be in the usual black font.
The problem comes in when you have many, many sub-folders/sub-files. In TreeSize one would have to search through the long list and individually do the renaming of all the 'red' font folders, could be twenty or thirty, whatever. A bit of a chore.
As all I care about in my particular case are the actual end files -- example, .mp3 files, or .epub files -- it's really nice to have Flatten that can dump all files into the base folder. Works great! EXCEPT when some nested file path exceeds 256. Then Flatten chokes.