Yet, Tim Wendelboe uses a Robur for espresso....
There's probably a milder result coming out of a flat that's more commercially accepted. And some would say a cleaner result better suited for cupping.
I've had lightly roasted coffee that tasted better with a conical but I'd probably choose a flat if given a choice between the two for different types of coffees and roasts.
Grinders are one of the keys to exceptional espresso. Discuss them here.