This is indeed very true, my Primera's auto wipers were spot on every time, they just altered thier speed depending on how much rain hit the screen and not how fast the car was going.

I have a superb, not an octy, but I have to say that I find the rain sensitive wipers pretty good on the whole.

Rain sensitive wiper work perfectly on my 1.9 Elegance. On the odd occasion with very light drizzle they need a little encouragement, but wouldn't be without them.

Keep your screen clean around the sensor though!