I decided to do an experiment.
I had a JLD installed in a 1960's Martin 0-16NY -- one of the lightest-built guitars Martin has made. Because it's so lightly built, the bridge has rotated, so I put a JLD in there to see if it would correct the rotation.
I'll ignore the bridge rotation for this discussion, and here's what I can tell you.
It appears to lower the resonance frequency of the top significantly (could improve bass response), it appears to reduce volume, and it appears to reduce some of the higher-frequency content.
The device with one brass pin weighs 40g.
The tap tone without the JLD: 231Hz.
The tap tone with the JLD: 192Hz.
That's a significant mass and a significant drop in tap tone frequency -- you should be able to get the same results by using brass bridge pins alone.
Here are some sound files for you.
With JLD:
https://www.box.com/s/aiqzwckp2bsnjbmmf4ce
Without JLD:
https://www.box.com/s/vr5bg0k4yn7cbvhjxo8y
Mic placement, guitar location, and playing style (bare fingers) should be pretty much the same in both. I used a Zoom H4n.