I installed them on my 1/2 ton GMC. I have since sold that vehicle, but I can comment on them. They made a huge difference in the performance of the vehicle. Especially when hauling a load in the bed. Whet got me looking was trying to haul bags of cement from the local Depot. The way the load mashed the bed down to the stops and the way it slopped from side to side while making a turn was amazing. I ordered them online and installed them myself. I loved the difference and suddenly my bed capacity went to 3,000 lbs. Never loaded it that much, but when hauling the next load of cement bags, it rode level and remained stout in turns and handled much better. This adds to safety when hauling your rig as well. Best 150 dollars I spent.
I have had them on all of my trucks. Camping World or JC Whittney has them the cheapest. I'm assuming this person isn't selling you them used. They do wear out early if not inflated enough. With the trouble of installing I would just go with the new.
The question is "What do you expect to achieve with the Ride Rites?". As Jim Shryker notes, they are excellent for leveling a load and help control sway. They do not increase the capacity of your rear springs or the GVWR of the vehicle, but they may help it handle better when heavily loaded.
Do you have a handling problem? If so, what is it? What do you carry/haul with the truck? With some background, we might be able to help determine if the Ride Rites will be beneficial to you. They are a good product, but not a panacea.