Oscillation-induced movement is plausible, but the maximum speed is limited by the integrity of the medium itself, which mean very slow compared to normal thruster. You're limited to few hundred km/h in the air and less than 60 mph underwater.
I have such propulsion in my fanon design, but it's a bit... handwavy. Theoretically, it's capable of subluminal velocity, but there'll
never enough energy to do that, so normally it's only used for extended supercruise (continuous supersonic dash in low altitude)
Good night.