Simple, nicely made, light, very pretty (contrasts beautifully with a standard spruce top), fits a standard 100mm sound hole perfectly, and does not have a tendency to fall out.
Compared with a thick rubber bung:
- it does not dull the acoustic sound as much
- it allows the top to vibrate a little more
While that would logically translate into lesser feedback busting ability, in practice, this little unit works beautifully.
Perhaps if you're playing in a loud rock band, you might want to use a thick rubber bung, but I wouldn't use a hollow body acoustic in such a scenario anyway.
In summary, I would recommend it wholeheartedly...