Now here is a brilliant invention for learning to play violin. A decal that peels off a backing and is applied to the violin as one piece beginning at the nut as a finger marker for first position. First Frets are made of clear, one-piece, self-adhering vinyl that lays flat on the fingerboard with no tapes. Four differently-colored and mathematically accurate stripes indicate the correct placement of each of the four fingers in first position. No more tapes that slip, stick, and, peel off! Thus, as First Frets present such a welcome alternative to cutting, measuring, and sizing individual tapes that may interfere with the left hand and also cause unwanted buzzing, I have been using them for about two years for violins sized 1/10 through 4/4, and I prefer them to tapes.
First Frets usually work quite well when students are playing on violins that have been set up well. However, on occasion, I have noticed buzzing if the action is set too low and the strings are very close to the fingerboard. This is because, when you stick a decal under the strings against the nut, this reduces the space between the fingerboard and the strings and thus the decal rubs against the vibrating strings during playing. However, this problem can be fixed if the violin's setup is adjusted for higher action. This can be accomplished either by having a violin shop "plane" (cut down) the fingerboard, or raise the nut.
Another issue is that, depending on string lengths, the lines may not be exactly accurate in their positioning on the instrument. Again, this depends on setup and each violin is slightly different. One way to address this issue is to move the bridge so that the string length matches the spacing of the First Frets.
Sliding the First Fret decal under the strings without having it stick to the fingerboard in the wrong place somewhere along the way is easier than expected, and can be accomplished by violin teachers and students alike, if instructions are properly followed. However, teachers and violin shops that are experienced with installation usually find them easy to install. Also, the strings need to be loosened to some degree in order to apply the decal. Thus, care must be taken to prevent loosening of the strings to such a degree that the bridge falls down.
From my experience, as soon as a student is able to play in tune reasonably well, these decals can be removed.
Though certain issues must occasionally be addressed, First Frets do work well for the majority of students and violins. And, unlike tapes, they do not slide on the instrument, nor do they peel off and leave a sticky residue, or make the fingerboard feel bumpy and uneven. Thus, they are a vast improvement over ordinary tapes and, in my opinion, are worth a try, especially given that they are quite inexpensive to buy.