I had Timbrens and didn't like them. It's like wedging a hockey puck in to level the load. I switched to Firestone "Air Springs" (bag) and have never looked back.
Inflating is so easy, my kid does it with a manual bicycle pump. With my 2500HD loaded and the heavy trailer, my truck is perfectly level and no porpoising down the 101 freeway.
They can really take a heavy load. I also run my truck off road all the time and I've never ever sprung a leak. They are ultra reliable in my opinion.