In short he has had a series of pretty terrible repair & support issues which for a pro photographer can be an absolute deal breaker.  Now Matt is in Australia, I have heard from US Sony users that support is much better here but it is something I mentioned in my review of the Sony A7RII.  You can hear all of Matt's thoughts in the video below.https://www.youtube.com/watch?v=apCc5JD4PYs