We use brass nipples on all our laced wheels (except on our the F2R-190) as part of our 'no-headache' approach. It is such a small weight difference (around 28g per set) that we rather lace an easy servicable wheel. Especially for bicycle wheels it makes more sense to focus on aerodynamics instead of weight.

As for the F2R-190, this is an ultimate lightweight climbing set, so we of course use alloy nipples for optimum performance and weight reduction.