I have used many stethoscopes (GMC 7037441) for those who want to know...i'm in the public domain anyway...
The main advantage of the (very) expensive litmann (and similar) stethoscopes is sound isolation...you can hear the lungs or the heart through any old tube, including the 5p NHS ones...but the more expensive ones have nice features like soft ear tips (very valuable after your first stethoscope induced outer ear infection), and you can't hear the drunk man in the bay next to you screaming while trying to listen for a soft murmur.
Of note in the picture above the 3d printed bit has litmann binaurals and a litmann diaphragm...and it's the binaural bit that makes the difference IMHO. The chest piece is not quite the point here.
I'd still like a go though...and the project ideas seem fantastic.
PPS it's an auroscope/otoscope.