I got unlocked for my 5 and locked for my 4s on that website. iphoneox.com says unknown and locked respectively. I stopped by t-mobile on my way home and picked up a sim card (they gave it to me for free). They said I would need a $10 activation kit to try it but I didn't think that was worth it, and thought I would see what would happen without it.
I put the microsim in my 4s. It began walking me through activation steps until I got "SIM Not Valid" and instructions to only use a supported carrier's SIM.
I trimmed it down to nano size and popped it in the 5. I got the same message.
It could just be because I didn't activate it for $10, so this isn't conclusive by any means, I was just experimenting.