Just out of curiosity how does Saw's OSTR work?
Is it still ratchet based, but just silent? Or does it work differently?
No, they're locked by hydraulic cylinders (that look just like car shock absorbers without the springs). One either side of the seat, both independently secured to the OTSR, so if one fails the other still keeps it locked. When unlocked the cylinder's fluid can flow through a valve in and out of a reservoir and so the piston attached to the OTSR is free to move up and down. When locked, the valve is closed and the piston can't move, so preventing the OTSR from moving also (or closed in one direction meaning the OTSR can only close, not open).
See third paragraph below:http://www.gerstlauer-rides.de/products ... ter-en-US/
The system has the advantage of being infinitely adjustable to the occupant size, compared to a ratchet system which only has set positions (which means the OTSR can be either a little too loose or too tight), with the disadvantage of being technically more complex.
B&M use these now on their wing coasters (like Swarm) and their workings are a bit more visible - you can see the tops of the cylinders and the connections to the OTSR at the top of the headrest, plus you can see the small hydraulic fluid reservoirs behind the seats (see pic below, black reservoir at very bottom, attached to red seat base support)
EDIT: A better image here showing the internal workings - note the gold cylinders in the middle-left of the photo, with the black reservoir (looks a bit like a black apple with screw cap on top) at their base.http://rcdb.com/897.htm?p=13383