I have one of the first models of Singer Quantum. Model 9240. Not the added Stylist title. It is the heavy duty Quantum, metal gears and built to last. The second version changed to non metal parts.
I love this machine. I has never given me one bit of trouble, sews with any brand of thread, smooth and quiet running. I bought it before I got serious into quilting. I think this is the best Singer made since the 301. I have the 301 and this Quantum is like sewing on it but with many more features. LOL The foot control runs on air pressure. I still don't know how that works but it does.