I don't quite understand the logic of this whole monorail plan, surely it would be far cost effective to build a conventional railway but to a lower standard similar to the former Goldsworthy railway or to Narrow gauge (Aurizon haul similar mtpa to Geraldton on NG), unproven technology plus the development costs etc what would they really save I assume it would require less earth works but substantially more steel and materials to build plus ongoing maintenance costs also how would they get around grade crossings, points, etc
The Aurizon Mid West operation is almost entirely on existing track, much of it used in the very early 1960s for one of the earliest iron ore export operations, preceding those in the Pilbara. Some of the track dates back many decades earlier. Some sections of track, but by no means all, have been completely rebuilt on a new alignment. Almost all these mines road haul to the nearest rail head.
The Lartigue system does appear to have worked, having lasted from 1888 until 1924 for the Listowel and Ballybunnion and its closure was blamed on the Irish rebellion. That system does look to be pretty lightly built and it could have been cheaper to build than even a narrow gauge line (certainly that is claimed).
The 1924 US system (see the link above) doesn't look convincingly cheaper than a narrow gauge mining railway but it might be cheaper to build in very rough country.
I can't say anything about MRL's proposed system, except that I can't imagine it being economical to build if it used a lot more steel than the Lartigue system.