That's true, but the labour cost is presumably already priced in to the cost of bought materials (while we live in the hell of a non-planned economy based on the extraction of surplus labour). The presence of this hybrid co-op/cottage bourgois production scheme, even at a single point in production is a massive improvement materially.

I assume once an actual plant is set up economy of scale will take cost down, but ideally that plant would be worker owned.