There are two significant differences between Snell M and SA specifications.
1; SA has a narrower field of vision specification. Some SA helmets are not for use on the street because of this limitation. There is also an optional SA with a wider field of vision.
2. The assumption in the impact test is that you hit your head ONCE when you fall off the motorcycle. With SA, you may hit your head several times on the roll bar and so more lighter hits are specified. Do you have a roll bar?
3. The fire test refers to the lining on the inside of the helmet. If the inside of you helmet is on fire, you are dead.
The debate between M and SA spec has gone on forever. I favour the M spec. wider field of vision. I see no merit in the fire spec. for DE drivers. My preference has always been for the M spec.