The Apple/Google app framework still needs a database of ids of people who have tested positive. If each country's app uses its own database, then they will not be interoperable. If there is a global database, fine, but who controls it? Google? Apple? Donald Trump? The WHO in collusion with China?
In theory the key lists* can be uploaded/downloaded from multiple servers or shared/distributed between servers or countries without risk of loss of any personal or location data - depends on implementation choices by countries.
Furthermore, by recording the first part of your postcode when you register, the NHS app can be used for resource planning. That seems like a huge advantage to me.
Not really, as the system has to operate seamlessly with manual contact tracing and the testing/isolation system. ATM it is is not even clear what the NHSX app user is supposed to do if they are alerted or have symptoms. The data should be collected from the (fully operational) testing system.
Since we are not able to influence these decisions, all we can do is hope that the app works well enough to help contain and manage outbreaks. If it doesn't then we have a fall back - even NHSX recognise that:
https://www.ft.com/content/d44beb06-5e3e-434f-a3a0-f806ce06576c(can't tell if this link is pay-walled or not - should be searchable)
- Essentially, they have contracted a Swiss company to investigate how the app could be switched to the Apple-Google spec.
ETA: Better link:
https://www.theguardian.com/technology/2020/may/07/uk-may-ditch-nhs-contact-tracing-app-for-apple-and-google-modelThe government has left open the prospect of ditching its own contact-tracing app in favour of the “decentralised” model favoured by Apple and Google after it was revealed that a feasibility study into such a change is under way.
After repeated warnings that the UK will be an outlier if it insists on using its own centralised app rather than relying on Google and Apple’s technology, rights groups and MPs said on Thursday that the lack of privacy and data protections could mean that the app would be illegal.
* Note that the lists are keys that have been in proximity to someone having symptoms or confirmed as infected - not ids of those reporting infection.