The upgrade is based on the regular MK3 so you'll have to reprint a new Frontplate, Coverplate and two other parts I designed and tested for the Piezo mounting. Baseplate etc. stays on the printer so you don't have to disassemble the rods again etc. Fanduct also stays the same. It is also possible to use the dragchain, igus or whatever configuration you had for the MK3 (beside BLtouch stuff because it is obviously replaced by the Piezo-system). Beside the print parts I'm providing a full detail guide, firmware & individual support.
I'm not the Piezo seller and I don't earn any portion of a sold sensor so basically: Yes you have to buy the Piezo BUT its the PCB only (24,99) (https://www.precisionpiezo.co.uk/product-page/precision-piezo-orion-pcb) NOT the whole Piezo Orion Kit. For the upgrade only the PCB is needed since my system includes a proper mounting solution of the sensor for my Carriage design.