I use a Canon 6D and Canon EF lenses for my "main" photography. I use a couple of Yongnuo YN-600EX-RT flashes and a Yongnuo YN-E3-RT flash controller for off-camera flash portraits. All the Yongnuo equipment has worked well for me with no problems.
I have a Sony a6000 that I take with me when I travel. The lighter, smaller form factor works well for travel. A couple of years ago, when I was deciding on which mirrorless to get for travel, I really wanted to get a Canon, but my research revealed that the early Canon mirrorless models were not that good—so I bought the a6000 instead. I don't currently use the Sony a6000 for any off-camera flash, just for travel.
Now that Canon has introduced a serious mirrorless camera, the M5, I'm considering selling my a6000 equipment and moving to the Canon M5. The Canon M5 has a standard Canon hot shoe.
If the YN flash equipment I have works with the new M5, I can have 1) my smaller form factor mirrorless for travel; 2) a backup to my 6D in a pinch for OCF, using all my EF lenses (with a Canon adapter); and all equipment in the Canon ecosystem.
I'm wondering if anyone has a Canon M5 and is using YN flash equipment. Any experience from anyone that shows that the YN flashes work/don't work with the M5?