You have to be much more accurate with your finger placement, with a fretted instrument you always aim for close to the fret, but it doesn't matter too much where you put the fingertip. With no frets every note you play is going to be flat or sharp unless you get it spot on, lines or no lines. I don't think the lines will make much difference, you'll either learn the technique or not, if you're looking at the lines all the time you're playing you haven't really mastered it, it's the aural feedback that's really critical.