Are there any advantages/disadvantages to the air bag option over the add a leaf option?

Air bags can be adjusted to match the load. Booster springs can't.

If the truck is sagging with just a shell on the back, it's time to address the springs.

Air bags are great for leveling out a vehicle when it's carrying a load, but using them to fix sagging springs in an unloaded truck IMHO is not the right way to use them.

A pals truck does the same with a leveling kit up front & load in back now.
Trucks are designed to have a low nose due to the fact when you put a load in the bed it rises & levels out.

With just the shell and an empty bed it sits within an inch or so of level.

But with the addition of maybe 300 lbs (stall mat "bedliner", extraction gear, hunting gear, and a cooler or two of deer meat)and it's sitting well back on the rear springs.

It handles fine as is, so if I can level it out with a typical load (using either option) would I be ok mechanically?

I know I could take off the leveling kit, but if the rear springs are shot (like RC says) it would still sag with a load. And I like the option of going with slightly taller tires when these wear out.

Load capacity varies by model but it will be a minimum of about 1600lb on any model. If it sags with just a shell and 200lb, you have a problem that needs fixing. Sagging like that will affect steering among other things.

Well, I decided to go with a Hellwig helper spring kit. Less than a hundred bucks, and relatively easy to install.

If that doesn't fix it, I'll add airbags.

Thanks for all the help and advice!

Why not just fix the springs?

Take that goofy leveling kit off the front end before you do anything else. Trucks sit slightly nose low for a reason. All the boy racer types want to jack up the front end with these leveling kits and they ruin the utility of the truck. I think they look stupid also, the truck ends up looking like a dog running with it's tail between it's legs.

Had Airlift bags in my Silverado..................never the phuck again