I liked it when things were simple and I didn't think every frigging piece of handwavium through.
The reactionless drive as original portrayed in Classic Traveller made interstellar government impossible. Any ship, even a 6 ton gig became a WMD because given a laughable fraction of its space for fuel it could get up near light speed. If you didn't like another planet aim a lifeboat at it from the Oort cloud and sit back, wait a few months and then blam! Enjoy the fireworks (wait a few years to see it from your homeworld or get it a week later on Pay Per View!)
Mega Traveller provided the first relief in the bombardment of reactionless drive projectiles. They said earlier maneuver drives only operated within 10 diameters of a body. Huzzah. That in effect produced an upper speed limit. Say you took your type S into a low earth Orbit and began blasting away at 2gs.
10d = 10*1280000m= 128000000m
d=1/2a*t^2 as anyone who read Robert A. Heinlein will tell you.
12800000 =1/2*20m/s* t^2
12800000 =10m/s *t^2
1280000 = t^2
(12800000)^.5 = t
3577 s = t
So you'd be humming along for about an hour which at 2 gees will result in a final speed of
3577 *20 m/s= 71.5 kps. Not exactly a planet cracker or unstoppable.
It also equates to a speed of 715 mm per turn if you still use the Classic Traveller starship combat system. Fast but not unstoppable.
Interstellar government is saved oorah!
But then MT decided that those limits went away above TL A.
But then Marc Miller said in T5 the more limited G-drive operated within 10 diameters (Tl A). A true maneuver drive operated within 1000d. Which let you boost all the way to the jump limit. Stupid G-drives made you cost for 90% of the way.
But wait you can ruin damn near anything with a little math. I know little math!
What if instead of beginning your boost from the LEO of a rinkydink planet you jump to a really biiiig star and begin your boost as close as you can get without melting your ship (not that you care all that much for it later anyway.)
Sol, a middling star has, a diameter of 1,280,000 km. 1000d is 12,800,000,000 km
with a run of 13 billion kilometers our Scout would boost for 13 days and have a final velocity of 22,600 km per second. That's 226,000 mm or 226 meters per turn in the space combat system. There isn't a game store with a backroom big enough to game that attack run out.
Dammit it yet again.
Seriously, a 100d limit to the maneuver drive lets you hit about 220 kps around an Earth sized world. A one THOUSAND diameter limit gives us the planet crackers back. Mind you none of this matters to the individual referee who can set whatever limits on the m-drive they want.