When JF’d the first hit does more damage, too. That is useful in juggles where b+1,1~f,N does 1 less damage than b+2~f,N, but using b+1:1~f,N will do 1 more damage than b+2~f,N.
In older Tekkens, b+1,1,2 was not NC whereas b+1:1,2 was. Now they’re both NC.
b+1,1,2 is -15 on block, so they can just block and launch you. b+1:1,2 pushes back and is safe on block. The last hit is high, though, so against opponents who know to duck, it doesn’t really make any difference. At least if you always use the JF version to make sure they have to duck to punish, you can b+1:1~f,N+3 to try and catch them in a juggle.
If you hit b+1,1,2 and it wasn’t JF, it leaves you at +1.