There have been certain cameras that a linear will affect the metering and the AF functions, in practical use when we were testing when I worked in the foto store, we found that it did not neccessarly have to do with the linear, but with the 2 stop light loss that gave the AF system problems, now these were not extensive tests and almost always occurred on the cameras that had slower lenses. I use a linear on my 9xi and don't have any problems with metering or AF functions....but as sterioma said, your mileage may vary.

Dave