It depends what you are after and what you want. Most less expensive products will provide more stability and support as loads are in the heavier end of the weight scale (Stable Load, super springs, etc). Air bags provide much more flexibility especially if you purchase the controller and compressor (this is what I have).
You don't describe what truck you have, but there's even the argument that if one has a dually you might not even need anything since the extra tires provide the comfort and stability of products you mention. You might even have the luxury of towing a few times and discovering you might not need anything. In my case, with my SRW, I needed something and the flexibility too, since I tow more than just my fiver. I am very happy with my Air Bags. It's like night and day for me. For example, I use 55-60 when towing the Monty, 20-40 when towing other, lighter trailers, or several settings depending how much I'm carrying in the truck bed (furniture, appliances, camping gear, firewood, etc.) and/or towing different trailers at the same time.
With an inexpensive load spring one does not get the flexibility to change the aspect and comfort. One has only what it provides and sometimes it can be a little stiff. The real importance to load stabilizers is to prevent sag and but one might lose some suspension travel or keep the headlights aimed too high from the sag. With my air bags and measuring that the angle is the same even when not loaded, my headlights do not elevate into oncoming traffic at all.