prepaid SIM cards

I’m thinking of getting my son a T-mobile prepaid. I’ve noticed that there lots of T-mobile prepaid pre-activated SIM cards on eBay at quite reasonable prices, some even under $10 with with about $30 worth of minutes. Is there a catch in this? Are they legit or they will be deactivated if found out?

Yeah, they are legit. I myself used eBay cards on t-mo, the catch is that you have to ad more minutes every 30 days or so, otherwise they’ll expire