The strength of f5less lies, IMHO, on being essentially a command line tool: you can do anything you want when a fs notification is triggered, and in addition you can reload web content using websockets.
Another strength is that the client reloading is very flexible and extensible, being javascript you can just change the f5less.js file to do whatever you want when a file with a certain filename is changed. I just encoded the basic and probably most common behaviours.
If you want f5less is something like watchr + guard-livereload, only command line and easily extensible.