It's a while since I read that trilogy (and the stories in the collection, Galactic North**, that relate directly to the trilogy), but I'm not sure making the lighthuggers "inertialess" was, strictly, part of the propulsion system (the conjoiner drives), more a way of making it easier to accelerate the ships (which did not achieve light-speed travel).I came across them in Reynolds writing in the Revelation trilogy and he kinda skimps over how they are supposed to work
** - The story where we get to see what's in a conjoiner drive is Weather. It may, or may not, be that story where the reader gets "some sort of idea" how those drives work, but it is in one of the stories in Galactic North.