Our good friend and client, Bruce Birnbaum went out and tested the teleconverter on his XC-10 (he has a C300 MK II), just to see how bad it might be knowing that features like this in the past left something to be desired......and he was pleasantly surprised:
Canon XC10 2X Teleconverter Test in 4K on Vimeo

Jim Martin
EVSonline.com