I haven't bought one as I can see other people having problems with theirs.
Just as I wouldn't buy anything else which has issues reported and which doesn't seem to have any sort of fix available.
I'm sure you are the same.
Or maybe not.
Alistair, it does not matter which camera model you get or from which company.... you can find "experts" who claim that the camera has problems and that there is a conspiracy. Sometimes these claims are true, like the Nikon oil-on-sensor issue, but in the vast majority of cases it comes from people not knowing what they are doing or having the settings wrong.
A classic example of that is the Tamron 150-600 which came out recently. A number of users were complaining that the AF on the lens would not work, yet they had the camera set into a mode where it would quickly abandon attempts at AF and just "give up", when all they had to do was to set the mode to "continue autofocus".
Auto-focus on fast lenses is very problematic, from any company. The in-focus range of some of those lenses can be less than half of a centimeter. Any forward/backward/up/down/angle movement after you have locked on focus will take you out of focus.. You really need a tripod under those conditions. One of my favourite lenses in the 100L... the DOF on that lens is miniscule... take a picture of a bee wide open and you can't even get the whole head in focus... it's DOF is that narrow! The depth of field calculator gives me a number of <1mm.
With a fast lens used wide open, AFMA is almost essential to good focus, yet few users AFMA their lenses, and of those who do, most do not do it right and may actually be making the problem worse.