Yes, it has been helpful.
I just bought my first violin, and as a guitar and ukulele player I am used to frets...! Well, this is a nice shortcut!
I made this adjustment in my own way. I did not loosen the strings of the fiddle (as I had tremendous trouble to get them tuned in the first place!) but I cut the "Don't fret" slip in two, unpeeled the backings and placed them under the strings. It worked just fine.
But the glue is not very good, I couldn't really manage the seal the sides properly.
Anyway, it doesn't disturb the playing. And it helps very much! In two days after the arrival of the violin I have made a huge progress in learning how to play and where to put my fingers.
(Without corona, I would have started violin lessons in January. Now as it is, I decided to start playing by myself. And this kind of position indicator is an enormous help, when you have no teacher to turn to.