That Piantor Pro looks similar to the Corne

It is; the stagger is a more aggressive, especially on the weak side of the hand, and of course it has that additional column, but you can see the inspiration.

A Corne would work for testing switches, for sure. IIRC I could have ordered the Piantor with swappable, but I was seduced - seduced, I say! - by those beautiful Chocs. It's my first non-mass-produced keyboard, and I didn't know any better. ¯\(ツ)/¯