Yeah I came to same conclusion after watching that video. The piezos sound so nasally. So it turned out the guitar player in my band had an Audio Technica pro 70.
When I tried it at home it was awesome, exactly what I was looking for. So I tried it on the next gig. I tried the in the F-hole position from the video. When I initially sound checked just the bass I thought man this is going to great. But that all changed as soon we all started playing. We are an all acoustic band, no drums. I have no amp on stage. Every one plugs into the PA. We don't really put it very loud. I thought there should be no problem using a mic at least from what I read about the issues other people faced.
But when we all started I was completely gone from the mix, could not hear anything ... except some huge boomy frequency when I played a C that would just ring. It seem like there was some interaction going on with the geometry of the place that the bass pointing a certain way would create a low frequency ringing on certain notes. It was very frustrating. at the first break I up the pick up back on.
So I guess my advise would be bring a piezo pick-up just in case
Here is a video of the same place, not the mic night so you can get an idea of at least one arrangement where a mic did not work at all: