Now on the subject of Full frame. I'm using this with a Canon M50. Which has a crop factor of 1.6. This booster gives a plus 0.71. Meaning that this crops 1.136. For example EF 50mm 1.8 with the adapter is an 80mm with the booster it is a 56.8mm and also drops the F down to 1.2.
The images and video were all shot using the Canon 50m 1.8 STM. the first image is with the speed booster with aperture at1.2. The second is with the booster at 1.8. The third is with the Canon EF-m to EF adapter with the aperture set at 1.8. The video is with the speed booster.
I have used this both for images and video. With video, I haven't really noticed any issues other than the motor makes does make more noise than usual and the autofocus seems slightly slower when changing the autofocus from one subject to the other. The 50mm is dead silent when used without the booster, so I'm guessing that this is the motor in the booster. When tracking I've noticed no issue beyond the focus motor sound.
Who should buy this and who shouldn't? If you already have a collection of EF Full Frame lenses, slap this thing on and Bob's your uncle. If you are just starting out and on a budget, the EF-M to EF adapter may be a better option because you can use both EF and EF-S lenses. EF-S lenses tend to be cheaper and THEY WILL NOT WORK WITH THIS SPEED BOOSTER.