As stated earlier, the difference between a mechanical gyroscope (spinning bicycle wheel on gimbals) and a laser ring gyro is significant. However, don't overstate this. Laser ring gyros are significantly superior to mechanical gyros in every way. They have drift specs that far exceed the best mechanical gyros, are smaller, lighter and more robust than any mechanical gyro. They can be sampled faster (1000 deg/s, 3000 deg/s^2) and combined with high quality accelerometers allows you to integrate to find your attitude.
The downsides of mechanical gyros far exceed their utility. They have inferior drift specs (friction sucks) and they're far less reliable. Just because something is old and mechnical doesn't mean it's better...