I have both the Eko Core (attached to an Littmann Cardiology Stethoscope and the Eko Duo. They both have great sound and hold on to their charge for at least a day. I have used both on children and adults detached from the stethoscope and wirelessly connected to an iPhone 11 and AirPod Pros. They both are amazingly similar to the traditional stethoscope with the added ability to record an ecg and amplification of sound simultaneously. These features coupled with the AirPod Pros noise cancellation make it easier to focus on faint lung and heart sounds in a noisy room. There is a slight delay in the sound transmission but the added feature of live recording of both ECG and heart sounds are great trade offs. These recording are easy to share among colleagues and great for documentation and review. All physicians, nurses and allied health professionals should have these tools to help keep themselves and their patients safe. JG