I got talked into putting Timbrens on 3 of the work vans. They did keep the vehicles more level with a heavy load, but that's the only good thing I can say about them. They effectively reduce suspension travel and all 3 had significantly rougher ride. I'd go with air bags, or just have better springs installed.
I had the Timbrens removed from one of the vans & had another leaf installed in the spring pack & it was a big improvement. As I recall, the added spring was not much cost difference than having the Timbrens installed.