I ordered one of the
JJBElectronics PPS-100's Tuesday. It came today. Fast shipping and he even gave me a USPS tracking number. It was $14.99, with free shipping. I haven't drilled a hole for it yet, but I taped it to the soundboard of my soprano, my Flea, a tenor and my guitar. It sounds great on all of them.
I tried plugging it into my Crate 15W practice amp and it was way loud enough and sounded good. I do not have a pre-amp. The sound is very natural, just like the acoustic sound of the particular instrument. I also plugged it into the 1/4" direct input jacks on the Zoom H4, and it worked great there as well.
Like the K&K, it is susceptible to feedback at loud volumes. Even though it was only $14.99 delivered, if you want an end pin jack and strap button, its an extra $8, so the cost begins to approach the cost of the K&K. Since both the K&K and the JBB are 20mm piezos, I suspect they sound the same. Both sound much better than trying to jigger up one of those Radio Shack buzzer piezos. I looked up the frequency response of the buzzer and its pretty bad.
I'm very sastified with the quality of the sound, and will post a sound sample, once I get a chance and have it installed permanently.