It is huge since it is reactionless thrust. Hook a plutonium reactor to it, pump in a few hundred or thousand kilowatts and the speeds you can achieve are astronomical. Things like to Mars in a week. To Jupiter in a week and a half. To Pluto in 2 weeks.
Of course, it remains to be seen how this effect scales in practice, but I believe the initial usefulness will be more in continuous moderate thrust over a long period than a top fuel nitro type of drag race spaceship.
The watermelons would sue for endless environmental impact studies saying the universe is too fragile for any radiation we might generate.