And you'd be wrong, it is high efficiency and high trust

The Orion concept offered both high thrust and high specific impulse, or propellant efficiency: 2,000 pulse units (Isp) under the original design and an Isp of perhaps 4,000 to 6,000 seconds according to the Air Force plan, with a later 1968 fusion bomb proposal by Dyson potentially increasing this to more than 75,000 Isp, enabling velocities of 10,000 km/s.[8] A moderate-sized nuclear device was estimated, at the time, to produce about 5 or 10 billion horsepower.[6][14]

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)