There is a WARNING in the box that states, “Please be aware that any lacquer type finish can be adversely affected if the rubber pad of tuner is left in contact with the finish for a period of time. ... SNARK advises NOT to use its tuner with any instruments having these types of finishes: Nitrocellulose Lacquer, Polyurethane, French Polish, Oil Finish or Gibson® guitars which have nitrocellulose finishes, unless you accept the risk of dents to the headstock.”
This message doesn’t appear anywhere on the seller’s page. Snark’s own website only has it available when you download the user manual. I use mine on a Fender mandolin and ukulele. It works fine and hasn’t caused any damage yet. The tuner works very well and Is easy to read. I have compared the mic to the vibration sensor and they are both dead on. I really do enjoy this tuner. But that warning has me paranoid that my instruments are going to get damaged. I wish that it was on the sellers page for this product. I hope this was helpful.