What can you expect when combining a recent camera, an older lens and some accessories that were never intended to be used together?
Actually, the results are surprisingly good!
I tested a number of Nikon F-mount lenses combined with a Metabones adapter and the new XF 1.4x TC on my X-cameras. The extra flange distance provided by the mount adapter solves the issue with the protruding front element of the TC.
The image quality results from the tested lens+TC combos turned out to be more than acceptable. A few pairs of 100% center crops to illustrate:
Combining the 1,4x TC with older primes may help fill some of the remaining holes in the X-mount lens line-up.
Definitely worth the try, and a lot of fun as well!
For an extensive discussion, see this article.