Moly will splinter when enough force is applied to it....it's slightly stronger than mild steel, allowing you to run a thinner wall tubing which saves weight, but personally for my drag cars I still run mild steel cages since I want the tubes to bend and not shard off in case of an accident. For a bumper I don't know if it matters as much since it will not possibly impact your body, but mild is cheaper and the difference in weight is negligable at this weight level.
I am in the market for a front bumper as well....any other pics of hte LEX front bumper from different angles? Looks good in the pic posted, just curious how it looks from the side or straight on. I like the ADD Stealth Fighter, but I think it sticks out too far, but I am not in love with cutting the front frame either to fit the RPG or WSI bumpers.