finally installed. only spring, no gear. i think it works fine without the gear, feels like the later E90's. need a bit more push to close it. the rubber feet makes black marks, just gotta wipe it off.
the slide part's cushion could be a bit softer, but the trade-off is def worth it. now i can drive leaning into the seat w the right elbow comfortably resting on the... as the name suggests, arm-rest.