Airbladders For The Rear Coils From Downey

I own a '94 4 Runner and was told by the tech crew at the local Dick Cepek shop that a great cure for the rear end sag on my 4 Runner is to install an airbladder in my rear coils. Downy makes the product and it sells for about $159. I was told that it has an air compressor that is controlled from the cab and can increase the lift as much as 2.5". Does anyone have any experience with this product?

Also, who has better shocks for highway and light off-road, Cepek or Rancho?