The Crown PZM 30D is a dynamic microphone that you can place on the inside of a piano or even on the floor. Its design is unique and allows it to pick up a great deal of specific sound. I have only used this microphone in the studio, as I believe that is the intended use for the microphone, but one could definitely use it in a live setting if they wanted to.
I've been using the Crown PZM 30D for about two years and I have found them to be quite useful in a number of different situations. The main use I have for the PZM 30D is to place it inside or on the top of a grand or upright piano. This picks up a lot of detail from the piano and will also isolate it really well if you have other instruments in the room that you do not want to bleed into it. I have also found this useful when recording noise or talking in a room if you place it on the floor as it will pick up everything in the room. The price of these is really reasonable for such a useful microphone. Having a pair of these is great and I use them all the time when recording piano and even sometimes for recording a Leslie speaker cabinet with a Hammond B3 organ. While these aren't the most versatile mics out there, as they can only be used for a few different applications, having them around is more than useful and they can really come in handy for the things it is good at. I can't think of any other type of PZM microphone that I could compare this to, as this mic is pretty unique. Overall I highly recommend these microphones for professional and home studios alike as they are great sounding and incredibly useful.