If they HAVEN'T been involved in an accident they're probably perfectly alright but the thing of it is, how would you know? That's something I wouldn't want to take a chance with.
All that stuff is so different now, I didn't know what half of it was that my daughter and sister in law have for my grandson! His car seat is like a 2-part thing - the frame of it stays in the car but the seat part comes out and you can carry him around in it. Then when they go somewhere, that seat part fits back into the frame somehow. It's good because if he's sleeping, they don't have to wake him up to get him in the carseat. And they had to explain to me what a 'co-sleeper' was, but it's a neat thing! Wish I had one when mine were little!