There are three Stemoscope Models: Stemoscope, Stemoscope II and Stemoscope PRO.
Stemoscope is the legacy model that was not designed as a medical device. If you expect to use the device for non-medical purpose, for example, use the device to listen to heartbeat sounds for fun, you may choose this model.
Stemoscope II is the second generation of Stemoscope. It was designed as a formal medical device and cleared by FDA. Some hardware improvement was made compared with the legacy model. If you plan to use the device for medical purpose, you may choose this model.
Stemoscope PRO is the smart wireless stethoscope designed as a formal medical device and cleared by FDA. Compared with Stemoscope II, Stemoscope PRO has additional functions and features such as direct transmission to Bluetooth earphones and noise cancelling, and is more suitable for professional use. If you are healthcare professional, you may choose this model.