The main claim of efficiency is because of the method of harnessing the energy of the explosion. Even if they are able to shape the plasma explosion as the article states, the pusher plate would only absorb 25-50% of the thrust capable energy. In contrast modern bell nozzles used for chemical propulsion are in upwards of 92% efficient, while the magnetic nozzles used by the fusion drive would be around 80% efficient.
As from the fusion drive itself, if you see the shape of the Conestoga, it is clear that it is not a Orion class system using fusion bombs. Furthermore, in the tech for the fusion drive module it explicitly states that the drive is also a power source, for the ion drive specifically, that rules out a Daedalus class propulsion system. The only conclusion then is that this drive relies on a tokamak fusion reactor that has some of its plasma leak out, and is mixed with regular hydrogen to increase its mass and thrust (while reducing its exhaust velocity), and directed outwards with a magnetic nozzle.
That in itself does not doom the Orion as a propulsion system however, what does is the practicality and the logistics of it. Orion is attractive on Earth, first, because it is a high end propulsion system that can be built with todays technology's, but the colony's have already mastered fusion which is much more potent. To put this into perspective, a fission reaction releases around 82 million Mj/kg, while a D-He3 fusion reaction releases a whopping 347 million Mj/Kg. Its clear why they wouldn't go for it, with a much more powerful and compact system already at their fingertips.
The second is that Orion provides a peaceful and scientific way to neutralize all the thousands of nuclear bombs stockpiled during the cold war, killing two birds with one stone you might say. But for the colony's, such bombs are few and far between, if and Orion program was started, not only would they have to build the spacecraft itself, but they would also have to mass produce hundreds, if not thousands of nukes for it. Such a feat would be a security nightmare, even if the governments of the colony's agrees not to use them as a weapon, (if not a MAD induced cold war could develop, and we all know how fun that is on a RTS) there are splinter factions out there, like the aforementioned masters, who if they got a hold of even one of the thousands of nukes, bye bye colony. I just don't see ether one taking that risk.
Those are the reasons why I am against an Orion class spacecraft in the Outpost universe.
