They are actually made of chrome moly. The weight loss is from the chrome moly material and because the heavy stock bushings aren't used anymore.
BDX has sold over 750 sets of them since 2008 alone. And I still sell many stock take off in our garage sale section every year.
Many people upgrade to the BDX rear arms because their stock ones are broken and bent.
Any suspension arm can be bent with the right hit, stock, bdx, anyones.
The comment on how the broke before they were even put on is a good one.
I had a flat land sled that I sold with to a buddy that now has a few thousand miles on it. It is a XF141. That sled has taken a pounding on the trails too. I know it's not a mountain sled, just saying it has taken several years now of beating.
Now I will say this, the very first batch back in I think it was 2008 was made of a thinner material, but nothing in recent years was made that way. Since about 2010 they have a thicker tube.
And as a matter of fact these suspension arms went through a Yamaha validation process and was sold as their upgrade kit for the Nitro from 2010-2013.
Just a few facts. But like I mentioned before, anything can bend or break. But in general the BDX rear suspension arms are a very good option.