I still play one of the old Manby fretted violins that Bob Bolton talks about. I play it because I like the sound rather than the fact that it has frets, plus it makes people look. As Bob said it has grooves where the frets are and was originally (1920s) made for learning on. One fiddle maker told me the tone would improve if I had a different fingerboard fitted but I like it. As for the frets, I don't notice them when I'm playing and I don't have any problems with glissando. You can feel the groove if you want to which helps learners but you can just ignore it if you wish and slide right over the grooves. Incidentally, I was told that in the 1920s the Manby company was the biggest violin making company in the world having factories in Melbourne, London and I think Paris and New York. They made orchestra grade fiddles as well. Does anyone know much about them?