I have had many teleconverters in the past 1.4, 1.7 and the previous 2 x versions of this teleconverter, using them with the 70-200 f2.8 Vr11 and the 300mm f2.8 Vr1 lenses for that extra bit of reach all bird and wildlife photographers crave. In the past the results when using the older 2 x converters have been very soft and disappointing compared to the 1.4 & 1.7 versions and even my 300mm f2.8 sometimes struggled for quick focus in low light conditions.
This new version however is a real step up, it focuses quickly with none of the hunting and provides excellent sharp images and as a result is a massive improvement on whats gone before. Although quite expensive it converts your 70-200 to a 140-400 lens at a fraction of the cost of a 200-400 lens with the loss of a few stops, but believe me at f6.3 or f8 the combination is as sharp as knife.
All in all this new version works very well, but check the Nikon lens compatibility before you purchase, as it won't always auto focus with many f4 + lenses.