I have been on a quest to find a better than just acceptable smart mount to use on my Canon EF 70-300mm L IS USM lens. I use an Olympus E-M5 Mk II (love the camera). Commlite Smart E Adaptor - I knew it had no autofocus, but was willing to give it a try for it's low price. Marginal performance on transmitting EXIF data. Lagged significantly in transferring focal length number trougout the zoom range. Shutter had a 3 second lag click to click. Was interesting, but not acceptable on any sort of outing. Jumped up the scale and ordered a Kipon smart with AutoFocus. Arrived with contacts on the lens side and no contacts on the camera side. WTF! Returned without any interest in them sending me a replacement that might have contacts on both sides Finally bit the bullet and ordered the $390 Metabones Smart Adaptor without Speedbooster. I had to do the firmware upgrade when it arrived, quick and painless, but you need a USB to micro USB cable to do it. Wow!!! Auto focus as fast as my native Olympus M43 lenses. Transmits focal length real time just like native lenses. Saves all the accurate EXIF data, including the fact that it is a Canon 70-300 L lens. I like the 5 axis stabilization in my Oly, but the IS in the Canon lens is better to use, at least for this zoom length. Excellent in lens stabilization out at 300mm. Wow, again! I paid $850 for a pristine EF 70-300mm L IS lens. It is a magnificent lens. The IS is superb. Now, with the Metabones Auto Focus smart adapter, the Canon lens runs like a native M43 lens. This definitely is a game changer with me over what I consider available lenses for my Olympus E-M5 Mk II camera. I cannot say enough about how quickly and accurately the auto focus works on this combination. Cost of the combo is right at $1250 for an L series quality 70-300mm setup with my OM-D camera. Any future Canon EF lens would not require the added cost of the adapter, so it puts exceptional quality glass, weather sealed, as a realistic competitor to native Oly M43 lenses. Size is a reason we often choose M43 cameras, but I had the 50-150mm Pro Olympus and it was every bit as long as the Canon 70-300. Everything is a give and take. I really expected to be left fully unsatisfied at the end of my trials. However I could not be more pleased with the Metabones performance, sitting between my EF L lens and my E-M5 Mk II camera.