There three things that turn tires into junk, time, miles and injury. Those are really pretty old. They would likely be fine for a dedicated offroad rig, I'm not sure I would run them on the road for long.
I've met a couple people that swear by them and there are a few people with older TJs and YJs that I wheel with that still have them and they work fine.
Seems like a good deal for $500. Tires do have a life span, but there are plenty of people that have classic cars or cars that they don't drive all that often with really old tires. As long as they aren't cracked and dry-rotted then they are probably fine.