One might even blame gravity manipulation for all of the futuristic propulsion achievements of Trek. The drive that warps space for FTL movement? Why, it sounds exactly like gravity manipulation technology!
OTOH, it may well be that gravity can be reduced or increased or directionalized, but it cannot be used for actually "bootstrapping" the gravity device into a state of motion. That is, it cannot be used for acceleration or deceleration as such, but only in combination with some other device that produces the accelerating force.
Some shuttles might have relatively mild inertia-nullifying fields coupled with a super-duper rocket which uses Newtonian principles but boosts those with gravity manipulation (and perhaps redirects the force vector so that the exhaust doesn't have to point in any particular direction). Others might use tiny conventional thrusters but would have a super-duper inertia nullifier.
The former might be better for craft that are expected to land on planets: it would be awkward to bring down a craft in windy conditions if its total inertial mass is two grams but it has the surface area of a large van. The latter might be what is used on purely spatial craft that never feel the wind, including all those TMP contraptions that had the exposed spatial docking ring (travel pod, both sizes of Probert shuttle, possible others). Or then there would simply be different performance characteristics for shuttles with differently "balanced" drive systems, but even the Probert ones could make planetfall, and even Class F would perform adequately in space.
Timo Saloniemi