Thanks Alan & mackguyver for the encouragement. I'm very happy with my x1.4 TC III.
I can see the x1.4 TC III on my 70-200 f2.8 IS II and x2 TC III on my 400mm f2.8 IS II for mid-to-long wildlife shooting
Now there's an idea -- actually I've been doing that for years - 1.4x on the 70-200 + 2x on the long lens has been my secret weapon for wildlife for as long as I've had both extenders. Actually it's been bare lenses in the dark, then 1.4x as the sun comes up, then 2x on the long lens, 1.4x on the 70-200 as the light improves.
EOS 1D X, 5DIII, M + EF 24 f/1.4II, 50 f/1.2, 85 f/1.2II, 300 f/2.8 IS II || 16-35 f/4 IS, 24-70 f/2.8II, 70-200 f/2.8II || TS-E 17 f/4, 24 f/3.5II || M 22 f/2, 18-55 f/3.5-5.6 IS || 1.4x III, 2x III