Phase detection AF is still available when using the XF50-140mmF2.8 R LM OIS WR with the 2x teleconverter mounted.
Contrast Detection AF is still available when using the XF100-400mmF4.5-5.6 R LM OIS WR with the 2x teleconverter mounted. Accurate focusing at super-telephoto focal lengths with shallow depth of field is possible thanks to the AF performed by the image sensor thanks to mirrorless cameras' "Live View".
The camera's optical image stabilization performance** is unaffected by the addition of the teleconverter.
Using the teleconverter with a weather-resistant camera, such as the FUJIFILM X-T1 or X-Pro2 mirrorless digital camera and the FUJINON XF50-140mmF2.8 R LM OIS WR or XF100-400mmF4.5-5.6 R LM OIS WR lens does not affect the weather resistance of the system.
The teleconverter's high grade metal exterior has been designed with the X system in mind. When attached to a compatible FUJINON lens, the two products appear as one single lens.