Does that mean that all the saved labour needs to be paid in advance when "buying" the technology

The point of the labor theory of value is not to try to recalculate everyone's wages so as to make them "fair" in some ideal society where labor is paid its "fair value" by some capitalist who is going broke for the hell of it.  Rather, it is regarded as a given that exchanges aren't "fair," that under capitalism labor isn't paid its "fair value" because the exploitation of labor drives the whole system, and that the best way to ameliorate this state of affairs is to not have capitalism, or capitalists.  The alternative proposed by ecosocialists is a union of free producers, in which the collective project of humanity is re-oriented to the goals of ecological integrity, or what Enrique Leff calls "ecological production."

"Imagine all the people/ Sharing all the world" -- John Lennon