When Space Toolkit came out (with the Tachyon Squadron kickstarter), I was glad it included what looked like a way to abstract space travel while maintaining Newtonian behaviour of spaceships. But now I'm taking a closer look at those either missed something, or have trouble understanding the game-mechanical trade-offs between engines (among other things).
I'm looking specifically at engine rules of the Mass Drivers setting, on page 146 of the Space Toolkit:
a ship can travel from one space to another on the space map in a few days, which counts as one exchange. Modify this travel time per exchange by steps equal to the difference between the ship’s Mass and Thrust, decreasing travel time if its Thrust is greater than its Mass, and vice versa (Fate Core, page 197). Thus, a ship with Fantastic (+6) Mass and Good (+3) Thrust would shift a travel time from a few days up to a few weeks or half a month.
Modify the distance that the ship is able to travel in one exchange by the difference between its Mass and its Impulse, so that a ship with Impulse greater than Mass is able to move one more space on the map per exchange for each step of difference. This reflects how longer periods of acceleration allow for the accumulation of velocity.
And looking at the above formula, and I don't see a game-mechanical reason to pick the low-thrust-high-impulse drive over the high-thrust-low-impulse drive.
In real life, the former has the benefit of generally having a higher ΔV, which adds up to a higher average and peak velocity over the course of the whole trip even despite low acceleration. When I look at the mechanics, a reduction of exchange duration seems to always result in a faster trip to the destination than an increase in the number of nodes crossed per exchange. (Specifically, as per Core 197, a step of time reduction offers at least a doubling of speed, and on average a bit more than that.)
Another way of looking at the increased fuel efficiency would be a drastic reduction in the rate of depleting the fuel stress track (minutes vs. weeks or more until empty), but I haven't found a mechanical support for that either. Maybe I overlooked it somewhere.
What are the game-mechanical benefit of impulse-oriented drives that represent the things they're cherished for, assuming literal reading of the rules?
It's pretty clear that by Rules as Intended, the impulse-oriented drive should provide faster movement on interplanetary scales (but not on small scales like launches, of course), however that's not what I'm asking about. Rather, I'd like to know if there are game-mechanical benefits of such drives in the literal reading of the rules that I may have missed - whether directly mentioned ones, or emergent due to any rules interactions I didn't think of. (If the rules are indeed faulty as they seem to be, applying changes/fixes will be the next phase of tackling this issue.)