My experience has always been positive. I've booked 4 or 5 flight+car booking and it is consistently much cheaper than exactly the same flights alone. I have always had the status at Avis recognised and tracked as it should.

You get the Avios you would for a flight, the Avios for the car rental with Avis, plus the bonus Avios for booking a holiday and the 3x Avios for paying on your BAPP.

I have even booked cars and hotels on their own; the hotel was cheaper and the car the same price through BA rather than direct, and you get the additional Avios.