Design: As with everything with Canon, these are really well designed and work perfectly. They even updated the color on these to help them match better with the newer version of the 70-200 and the 100-400, so that is a nice bonus. It is light but still has some good weight to it so you can feel the quality construction.
As for the use of this, it works perfectly with the EF lens series. I can also verify that it works with the RF-EF adapter on the mirrorless cameras. REMEMBER THAT THIS WILL MOVE EVERYTHING UP ONE STOP ON THE CAMERA and EFFECTS THE AUTOFOCUS POINTS.
MICRO-ADJUST THE CAMERA TO ENSURE BEST FOCUS or, like me, your photos will just seem to be slightly soft on focus
Cost: I purchased it for $340, currently $429
Overall: I am a Canon equipment user and this is just another in a long line of great products
Positives:
++Cost (but I got it almost 25% off)
++Design
Negatives:
--Autofocus effects
--F-Stop adjustment
Would I recommend: Absolutely/Borderline. Absolutely I would buy it again, borderline if you are not sure what to do with the other settings on your camera.
Photos attached with the adapter on