Until I used the 300GM, the 70-200II I found to take TCs better than any other Sony lens.
I only borrowed it from a friend for a day to test out. I never owned it.
I only did a little bit of shooting with the 1.4TC as I was mostly curious about how it did with the 2xTC in comparison to my 100-400GM.
I can say that AF even with the 2xTC was excellent so you should have no worries about AF or IQ with the 1.4TC.
My 100-400 at 400mm was sharper than the 70-200II/2xTC at 400mm when comparing test shots back on the computer. But AF was pretty close.