Although I have not used one, I know people who do. They like that they can simply cut in what ever direction they want, but cut a healthy distance from the line. I brought my Fret saw and cut very close to the line. I figure that it takes more skill to cut close to the line, but I can easily cut far from the line so I would prefer the smaller blade (which is why I use it).
I can cut pretty close to the line, but, I don't think that I have decent fret saw skills.