Just spoke to the store I use for AMflow. They sell many other Brands that use the M2 Motor, while sales have slowed slightly they have sold across all the Brands close to 100 bikes that use the M2. Not one single issue with the speed sensor as you set out above. Same for any other motor related issues. I suspect this is propaganda put out by other brands who sales have been completely destroyed by Anflow and DJI.The speed sensor isn't part of the disc, it's in the frame. The slots are just how is gauges speed. That's not the actual sensor. Been quite a few people getting speed sensor issues on the m2s. Which is disappointing as that was an issue on the 1st gen. Zero parts in the UK to get it replaced current.
The motor rattle thread on this forum is also concerning. Another thing they were meant to fix on the 2nd gen