used to have a Tubular OPC, 25 years ago was actually quite decent..
still need to use 1/2" pedals , though there is a 'knee saver'
1/2" to 9/16 adapter , now .. widens the Q [feet further apart], of course.

fine for single speed or rear hub gears. internal or external .

OPC's Bearings are cheap and races bang in and out easily.

I'd say if you want aluminum Crank arms .. the Adapter rings
to make it possible to fit a regular type BB is the way to go.