It is effective mainly if you will want to wind down the windows a little on a rainy day. Which means you don't intend to switch on the air-con and want some ventilation, at the same time to shield the rain from entering the car.
Noise is definitely inevitable. But it will depend on your threshold for noise. Before I fixed it, there was very little wind noise, maybe like less than 5% in high speed. After I put on the deflectors, the noise increased to maybe about 15%, with the windows up. Thus it can get a bit 'noisy' if you wind down the windows slightly.