If it was a no-name offering we'd be worried about a stem weighing 125g, but Salsa have a reputation to uphold.
We've been giving this a pretty hard time on a rigid one-speed bike for two months - lots of big leverage on climbs and lots of thuds on rocky singletrack - and it's held up nicely.
The stem is made form M9-grade Scandium alloy, said to be superior to the 7075 heat-treated aluminium used for many stems. We like the replaceable stainless steel barrel thread inserts which will reduce stress risers in the stem and steerer, and the tapered bar reduces stress on the light bars that most people who buy this will use. There are an impressive 24 size options and the price is reasonable too.