I'm a guitarist and used to frets, so this is an amazingly useful tool.
Negatives:
I'm a little disappointed that the sticker took with it some of the white from the paper sticker backing, so there are white spots of paper on the back of the sticker and on the fretboard, which don't look great.
Also, the colors need to go. Silver, white or even a subtle coal-black so that the audience can't see the very colorful strips. The sticker should also be matt so there's no sticker shine.
To clarify, it's a very good product, but I'd love to see these small changes.