Hello. First of all I am not convinced about the weight comparison. A single spanish bearing weighs about 39 g. So it depends on which spacers you use or if you use a sleeve between the bearings.
I once tried the KHE plastic bearings and these have an shell made out of aluminium. In the end the weight saving was only about 20 g. And the were supposed to be used without a sleeve. But due to this I could not tighten the crank arm bolts enough (otherwise the crank was hardly spinning anymore) so they got loose every 15 min of riding... It did not work out for me at all.
Maybe these are different.