Hi, it was a long time ago but I worked on this and can answer high level questions.

https://www.nature.com/articles/s41598-018-38096-z

Man, is this still sexy science !

In a parrallel universe, I am still be working in that domain (I was in Silvestro Micera's lab (he did similar kind of feedback for the hand) for my Master's thesis - also a long time ago; it didn't go so well due to an expectation mismatch from both myself and my supervisor)(I now work as a software engineer... pay and oppotunities are better).

If I understand correctly (I only skimmed your paper), the method you used is to take a muscle, cut it in two lengthwise, use those as a pair of muscle to graft, then put two nerves close to it and pray for re-inervation. Then you use EMG as a basis for your signals.

- Help my brush up my EMG knowledge: what's the tradeoff in choosing the muscle ? For a human case such as the one provided in the link, do you have the same signal quality choosing a smaller or bigger muscle ?

- I assume you're using intramuscular EMG (you're doing surgery anyway, so you might as well put some electrodes). How does this behave over time ? I had some experience in brain-computer interface, and I know scar tissues and the like is a real issue that can come up over time.

For what percent of trial participants did the interface function well enough for normal function?

Did you find any evidence, even anecdotal, about alleviation of phantom limb symptoms? I imagine it would be complete and instantaneous but I'm not an amputee with any experience.