In reply to Tim Bevan:
I would worry more about the lower hardness of the Al and the lack of wear resistance compared with steel. The steel tips can be sharpened. Dinged threads impeding placement and scratched cores impeding clearance is how these will fail.
Lightweight screws are great for their designed purpose, lightweight alpine stuff, occasional use but as a regular workhorse they won't last long.
However, they look cool on your harness. the inbuilt obsolescence keeps the manufactures and gear shops happy.
When looking to save weight on gear, look to your midriff first.