Then he should avoid LiquidMetal. It's density ranges from ~7.4 to 8.0 grams per cc, depending upon the alloy. That's right in range with other cast steel alloys, and about 2.5 to 3 times aluminum (and about 4 times magnesium).
Note that casting Al and Mg and AlMg alloys is rather well understood, and depending upon alloy selection, you can get Ym values close to LiquidMetal with about a 3X savings in density.
LiquidMetal's alloys (note, there is no alloy called "LiquidMetal") can be cast much thinner in more complex shapes. Estimates show half the weight for a MacBook Pro re-cast using these alloys.
Note that casting Al and Mg and AlMg alloys is rather well understood
As are the rather serious limitations that LiquidMetal's alloys don't have.