Why would anyone make custom derailleurs when modern electronic shifting works extremely well? It’s a bit like driving a car with manual transmission even though the latest automatics are very sophisticated. It’s about being involved in the operation of my bike, rather than just pushing a button. There’s a joy in feeling the gears engage perfectly because I – and not a computer – timed the shift perfectly.
...
And then I get a crunch, because even the best systems don’t shift that well with very high power outputs.
....
I don’t need to shift under load
https://www.renehersecycles.com/my-pbp-bike-derailleurs/
@amey