I did not realise these FBR blocks were twice as large as a...

I did not realise these FBR blocks were twice as large as a besser (cinder) block thank you for the correction .
You mention faster "(1 day compared to 2 weeks ) " how did you come to that conclusion ?

While less waste may be an admirable attribute , is it actually a high priority when making a business decision for running the ruler over a business proposition , given the amount of skip waste at building sites and the relatively low disposal costs per tonne of waste (here $15 a tonne) I doubt if it rates highly

My supposition would be a contractor will look at the opportunity cost of the FBR machine compared with an alternative use of using that capital , that opportunity cost will be dependent on the contractors skill sets and the local demand for services .
for example if the contractor did a comparison of buying a FBR machine for 400k compared to buying a 32 tonne excavator for A$400k and could charge himself out at A$400 an hour for 2000 hours a year that would bring in $800K a year in sales and would only be doing 1 shift a day rather than 2 shifts for the FBR machine so life style decisions would also come into the mix