expiring car seat?

The infanct car seat doesn't fit my daughter any more, so I am buy a convertible car seat. My hu*****and's friend gave us a used one that his son had been using for years. I noticed that the car seat is expiring very soon. I feel hesitate to use it. My hu*****and thinks that the expiration date is more like a commercial thing, because manufactures want to make more money. I googled "why car seat expire?" The answers  are mainly two: the safety standard has been imporving, so buying new one is giving you the opportunity to get the better one; the material is wearing off.

Shall I insist to buy the new one?