Reviewed in the United States on April 18, 2022
I was a bit skeptical, but it worked like a dream. I had a hairline fracture in the back of a $5,000 acoustic from humidity and temp changes. I moved the guitar to a more temp stable room in my house, dropped in this humidifier, and after about 5 days the crack has vanished entirely. The wood re-humidified and swelled ever so slightly (which was my goal, of course) to perfectly fix the hairline fracture.I love this product because it does what it was made to do very well. My guitar was seriously dried out and I needed to re-humidify it because it's playability and sound had degraded to an almost unplayable point. I had been using another product that you insert between the middle two strings with a moist sponge inside. But that product may work to keep a guitar humidified but not to recover a dried-out guitar. I bought the Vertigo Single and with only one fill and about a week, my guitar was playing significantly better, and the fret buzz was gone.
On my second fill of the Vertigo Single, I mistakenly soaked it longer than the recommended 20 minutes and overfilled it causing some of the polymer gel to be forced out onto the exterior. I wiped it off and let it dry out for a day and then put it back in my guitar where it continued to work well. Lesson learned...don't lose track of time and allow the Vertigo Single to overfill. Highly recommend the Vertigo Single Guitar Humidifier.