It's not a who. It's an Australian maufacturer of probably the best aftermarket suspensions. They are known for superior ride and handling (better than new), where as other aftemarket suspension companies are just the opposite.
Add a leafs are ok, they always seem to ride a little rough. You are expecting one add a leaf to help out the multiple peices that have lost flex over the years. Have you ever heard of the ZUK mod? It uses a coil spring over the rear axle. very simple to do, and gives about 2-3 inches of lift in the rear and a much softer ride. I have done it and I must say, it looks and rides much better.
If you want more info on it, look up ZUK mod on yotatech.com.