I was able rent in Sony Center Zürich following equipment :
I test it with my SONY FE 70mm - 200mm F2.8 GM OSS lens
Plan was to use it during my ZRH plane-spotting session. But morning on 26.10.2019 wheather was foggy and use of teleconvertors for photographing airplanes take off or landing was not possible .
:-(
After session was finished I did some photos from visitors desk - here you can find sample photos done with:
SONY FE 70mm - 200mm F2.8 GM OSS
SONY FE 70mm - 200mm F2.8 GM OSS and 2x tele convertor
SONY FE 70mm - 200mm F2.8 GM OSS and 1.4x tele convertor
Review conclusion: Looks, that both tele converters are working fine. I was not able recognize any "dramatic " lost of quality.