Hey all - I have the firestone bags in the back springs. They only give about 1" of lift (after my RRO - OTT 2" lift), so 3" total - when empty. When loaded down with 200 - 300 lbs of off-road and camping gear, I sink down about 1" on the springs w/o the bags, so these put me back up to about 2" higher than I'd be w/o them, under load. That 2" makes a big difference to my tire clearance (33 x 10.50's) and articulation.
The catch is they're awfully finnicky. If they're not inflated, they tend to move around a lot inside the spring, because there's nothing holding them in place. They'll get twisted, then you hit a bump, the airline gets pinched and springs a leak. The solution (after a couple replacements!) is that you HAVE to keep at least 20 psi in them at all times. I was keeping 10 psi in them, but that's not good enough. No big deal, but it does make the ride a little rougher. Max is about 40 - 45 psi. Therefore, if you get them, I recommend you spring for on-board air, and a gauge and valve kit, so that you can adjust them easily from inside the cab. I've got this, plumbed to my ARB compressor, and it works fine - just give it a little shot every week or so to keep it at 20 psi.
BTW, when wheeling once, I had a slow leak in one, and didn't notice it had deflated. The other was fully inflated (~45 psi). We were stopped, with my truck at an angle, hooking a strap up to a buddy. I gave a small kick to my rear tow hook for fun, and all of a sudden a very loud 'gunshot' went off! We were all looking around for a hunter, and couldn't figure out what it was... turned out my other bag had popped!
Overall, I'm happy with them (now...)
