Here's the full list of bonuses
does that mean that I need to spend less mass, and with the same build power, will I finish producing of an expensive unit faster?
You will spend less mass but the build time is unaffected. A factory which usually would draw 4 mass/s with a 25% mass discount will instead draw 3 mass/s building the same unit.
Also note that these discounts are for the factory build power only. Any engineers assisting the factory will not receive any benefits.




