They should use their purchasing power to force companies into having better software.

Have you ever seen good software written by a hardware company?

This is (imo) the same debate as funding for science. Yes, big pharma seems to show you can have privately funded science - but this is a small corner case for science as a whole, and they still make their work public - its just copyrighted.

Imagine a pharma company announcing a brand new cure for "baldness" - but people would have to sign NDAs, could not remove their hats in public and so on.

"Deal with FOSS" is an interesting way of phrasing "Not keep secret how an implanted medical device works".

There should be a fundamental right for patients to know this, otherwise they effectively don't have bodily autonomy.

Outside of emergency scenarios, they can forgo the treatments they don't feel are well enough explained, so I'm not sure "don't have" is entirely accurate.

They had bodily autonomy at the time they made the decision. They gave it up in exchange for receiving the treatment, and thus no longer have it; the "don't have bodily autonomy" phrasing is accurate. The fact that this was a voluntary decision which they were perfectly entitled to make does not mean that it wouldn't have been better if they had another option which allowed them to receive the treatment without giving up their autonomy.

Merely not being provided with documentation for how the device works and how to control it I could overlook; after all, we don't even have that for the bodies we're born with. Everything we know about how we work is reverse engineered. But the patient is most likely prohibited by law from reverse engineering or otherwise tampering with this device which is now part of their body, and that I cannot condone.

Voting with their feet/wallet/choice of medical procedure? We have rights and regulations because these individualist methods have again and again been proven ineffective.

I guess FOSS advocates have a different definition of "best".

I assume they meant code directly funded (i.e. written by a subsidiary of) the NHS, not proprietary purchases. Seems that's not the case here though, the device is proprietary.

See my comment above. The NHS are implanting devices / software created by an American company, and use the supplied telemetry systems to get medical data. I have no evidence that the data is also sent back to the US company, especially given that the NHS are paying for the bandwidth.