Works only, not best. A Dora's immobile in a spinner, last I checked. Actually, space jets are, I believe, the only bit of the four non-ground propulsion items (flight, arc, hover, space) that only adds to space flight. Everything else gives at least a little bit to space travel along with their primary effects.
Really, the poor things seem mostly useless; flight jets do about the same thing for space travel while eating the same weight/slot cost. I guess you could stack them on top of flight jets to get an extra kick in space jousts, but that's... a little excessive. S'already not particularly difficult to hit 2-3 hundred speed units with a mech loaded down with flights/arcs. Maybe for a specialized inter-spinner transport mecha, I'unno.