Used baby mattress?

Katie
I have a friend who is getting rid of her crib mattress for $20. It's a Royale II by Colgate. Exact model is no longer sold. Her son is 2-3 now. Do you think it's okay to use? I see stuff online about not using used mattresses bc of SIDS and want to be careful. She's super clean and I know it's well cared for and in excellent used condition. Thoughts?