[tdq]

I wondered the same thing.
I went ahead and bought one, just like the picture the OP posted, and installed it in my parlor. Installed, with significant EQ, it sounds ok, but on its own it sounds awful.
I also have a JB which I've put on my resonator - a very different guitar, to be sure. It still needs a decent EQ but the unprocessed sound isn't awful. One of these days I'm going to mount them both on one guitar and do a proper comparison...

It's just a ceramic disc on a copper plate, how different could it be? I had a chat with a guy at work who is pretty knowledgeable on things electric (he makes his own pedals) but not on piezos specifically. We though maybe its just better QA on the more expensive options, but that's just a guess. It's definitely better build quality for the non-piezo parts. One of the discs came loose inside the plastic mounting on the cheaper piezo so now it buzzes. You get what you pay for...