I've recently scored a double edge LR Baggs system from e-bay which I had planned to use for a gk midi pickup in my 1570. I also wanted to get the piezo sound in the same guitar, so I installed both systems after routing the guitar. I found the LR Baggs preamp is DOA (probably the reason it was being sold on e-bay in the first place lol) -- but the piezos do work, although not nearly enough power to "keep up with" the magnetics.
Anyhow wired together w/o the preamp they sound ok, when mixed with the bridge or middle pickup they sound very similar to my alvarez acoustic (it has a cheap piezo in it) hooked up to the same amp. It also closely resembles a good acoustic simulator, like the kind of sound metallica used in some of their early music.
I know my setup isnt exactly what you'd get in a
production model, although Im sure the preamp mostly just beefs up their sound a bit. I have another Ibanez electric which I installed a shadow piezo trem into, and the doube edge blows it right out of the water. The double edge is not the be all end all of piezos however, its still a piezo and thus it still gets "that piezo sound".
-Greg