Here is my code: https://github.com/mateuszbaran/FunManifolds.jl . I’m still setting up CI and docs, many things are missing and there is still quite a bit of code to be published later. I think product space is, at the moment, the best demonstration of some tricks I’ve used to get good performance.
I agree that details of a common interface should be discussed somewhere else, maybe an issue in Manopt.jl?
About distinguishing manifolds and metrics, that’s something I was thinking about that some time ago, and my conclusion was that so few things remain the same when changing the metric that it’s best to make two completely separate implementations.