If you turn off sustained burn you can easily exit it anywhere you want - for crossing 'rapids' without getting dragged an emergency burn is needed, though if you don't want to you can go upstream a bit and cross normally (again turn off sustained burn). Sustained burn raises top speed but lowers acceleration, so you get pushed more easily by things like slipstreams, coronas, black holes, pulsars, storms.
So, as far as I can figure, this doesn't work. I cut off sustained burn but leave the ships following the path to the destination, which is basically directly across the slipstream 'river'. I get washed down the river, and the ships never make any appreciable progress across the river. Very frustrating.
Secondarily, one suggestion is to have the 'rivers' visible in the map, at least once you've cleared the fog of war, so you can figure out how to best avoid them all together. For me, this new feature took a game a loved to a place where I'm considering shelving it. The long-distance travel mechanic was already frustrating due to how much RL time it takes, and this just ratchets the frustration up without actually providing any real incentives, like improved exploration rates or loot hauls.
EDIT: OK, it does work....sorta. For really thick 'rivers', the pressure is low enough that the ship can cross. But for thin, fast ones, you are just merciless, so you basically have to scout out the end so you can go around, and since it doesn't show on the map (tab), you have to do this over and over. Still more frustrating than anything in my opinion.
