The most notable difference that I can state about the M steering wheel compared to he stock wheel are as follows:
1. Thicker diameter (7mm from what I have read)
2. Softer padding on the wheel
3. Softer and higher quality leather wrap.
I only expected the thicker wheel from my initial research which was already appealing enough. After receiving the wheel, I immediately noticed the much higher quality leather and softer padding. Otherwise everything else seams to be equal. The airbag clicked into place perfectly and changing the wheel was a breeze. The pull-pull paddles are great and functioned exactly as expected. I prefer them much more and the push-pull design of the stock one. Hopefully the pics show the differences that I have stated (other than the softer padding!)