This was a risky purchase on my part due to the fact that I was not buying it for a Kala U-Bass (for which it is specifically manufactured.) I was, in fact, buying it for use on my Sigma TM-12E, a half-size guitar. As advertised the product was slightly too small for the sound hole on my guitar. However, this was an anticipated and accepted shortfalling. It took a few roles of tape around the circumference of the Feedback Freezer to bulk it out just enough to sit in the sound hole of my guitar. In terms of its use, I have no complaints. I had not experienced feedback problems before and this product was bought just as a precautionary based on a recommendation. However, I cannot fault the product to date.