Straight Talk + unlocked iPhone vs. Official Straight Talk iPhone - not equal!

I can only say this I got a straight talk iPhone 5s yesterday. 12 April. Everything works here in the Wilkes barre / Scranton area of Pennsylvania. Within 5 minutes of activation the mms including sending pictures worked I get lte I have not missed a call to see if visual vmail work..
My phone says TFW on the top left when I turn off wifi it says LTE here is my speed test wifi off.

Now here is my home screen showing LTE
This is iPhone 5 s. From walmart on straight talk. That's all the info I have, so far it's working fine in my location!!

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Update
After more testing this morning
I took the Straight talk sim out, put in a AT&T sim it registered it and got signal
same signal LET shows up when wifi is off
I put a VERIZON sim in and it would not activate invalid sim

I then took those both Sim cards and put them into a AT&T iphone 5s and got the same result

So for my area I am going to conclude the straight talk iphone 5s is LOCKED to at&t because the Verizon sim would have worked if it was not..